DESCRIPTION PROCESS FOR PRODUCTION OF 5'-GUANYIIC ACID Technical Field [0001] The present invention relates to a method for producing 5' -guanylic acid and a novel microorganism used in production thereof. 5-guanylic acid is useful as seasonings, medicines and raw materials thereof Background Art [0002] As methods for industrially producing 5'-guanylic acid (guanosine-5'-monophosphate, hereinafter also referred to as "GMP"), methods wherein guano sine is produced by a fermentation method and the obtained guano sine is enzymatic ally phosphorylated to obtain 5'-guanylic acid have been known (Patent Documents 1 to 4). [0003] In addition, a method of production wherein a microorganism belonging to the genus Escherichia having an increased GMP synthesize activity and Brevibacterium ammordagenes having a high activity to biosynthesize adenosine troposphere (ATP) (hereinafter referred to as "regenerate ATP"), which is generated by glucose metabolism and necessary for the synthesis of GMP from 5 -dactylic acid (XMP), are cultured in medium containing XMP and ammonia or glutamine, and GMP is generated and accumulated in the medium by converting XMP to GMP with high efficiency has been known (Non-patent document 1). [0004] Meanwhile, methods for producing GMP by a fermentation method have been suggested For example, Patent document 5 discloses a method for producing characterized by culturing a mutant strain of the genus Bacillus having adenine auxotrophy and showing resistance to decoyinine or motioning sulfoxide, as well as ham ability to pxxiuce GMP, followed by collecting GMP generated and accumulated in a medium. Also, Patent document 6 discloses a method for producing GMP characterized by culturing a strain of bacteria belonging to the genus Escherichia having ability to produce inosinic acid (inosine 5-monophosphate, hereinafter referred to as "IMP") wherein two types of 5-nucleotidase genes are deleted and IMP dehydrogenate gene and GMP synthesize gene are amplified, and collecting GMP generated and accumulated in a medium. Yet, in general, direct fermentation of GMP does not provide sufficient yield and is not necessarily practical compared with the above-described enzymatic method. [0005] Thus tar, no case producing GMP from IMP as a raw raptorial by using bacteria belonging to the genus Escherichia with enhanced activities of IMP dehydrogenate and GMP synthesize has been reported Patent document 1: JP 07-231793 Patent document 2: JP 10-201481 Patent document 3: WO96/37603 Patent document 4: JP 2001-245676 Patent document 5: JP 56-12438 Patent document 6: JP 2002-355087 Non-patent document 1: Tatsuro Fujio etal., Biosci. Biotech. Biochem., 1997, Vol. 61, No.5,p.840-845 Disclosure of the Invention [0006] An object of the present invention is to provide a method for producing GMP from IMP using a microorganism and to create a novel microorganism to be xised in the melrMxI which can convert IMP to GMP with high efficiency. [0007] In order to solve the above-described object, the inventors of the present invention intensively studied and found that by using a microorganism belonging to the genus Escherichia which has been modified so that IMP dehydrogenase activity and GMP synthesize activity are enhanced, IMP is converted to GMP with high efficiency and at high speed, and also succeeded in creation of a novel microorganism capable of converting IMP to GMP efficiently, thereby completed the present invention. [0008] It is an aspect of the present invention to provide a method for producing 5'-guanylic add, comprising: generating 5'-guanylic acid by reacting inosinic acid with a microorganism having an ability to convert inosinic acid into 5'-guanylic acid; and collecting 5'-guanylic acid, wherein said microorganism has been modified so that inosinic acid dehydrogenase activity and 5'-guanylic acid synthetase activity are enhanced. It is another aspect of the present invention to provide the method as described above, wherein inosinic acid dehydrogenase activity and 5-guanylic acid synthetase activity are enhanced by increasing expression of guaB gene and guaA gene. It is another aspect of the present invention to provide the method as described above, wherein said guaA gene encodes a protein selected from the group consisting of: (A) A protein comprising the amino acid sequence of SEQ ID NO: 2, and (B) A protein comprising the amino acid sequence of SEQ ID NO: 2 but which includes substitution, deletion, insertion, addition or inversion of one or several amino acids, and has 5'-guanylic acid synthetase activity. It is another aspect of the present invention to provide the method as described above, wherein said guaB gene encodes a protein selected from the group consisting of: (C) A protein comprising the amino acid sequence of SEQ ID NO: 10, and (D) A protein comprising the amino acid sequence of SEQ ID NO: 10 but which includes substitution, deletion, insertion, addition or inversion of one or several amino acids, and has inosinic acid dehydrogenase activity. It is another aspect of the present invention to provide the method as described above, wherein said microorganism has been further modified so that one or more genes selected from ushA gene and aphA gene do not function normally. It is another aspect of the present invention to provide the method as described above, wherein said microorganism has been further modified so that one or more genes selected from purR gene, add gene and purA gene do not function normally. It is another aspect of the present invention to provide the method as described above, wherein said microorganism has been further modified so that nagD gene does not function normally. It is another aspect of the present invention to provide the method as described above, wherein said microorganism is selected from the group consisting of bacteria belonging to the Enterobacteriaceae family, Bacillus bacteria and Coryneform bacteria It is another aspect of the present invention to provide the method as described above, wherein said microorganism is an Escherichia bacterium. It is another aspect of the present invention to provide the method as described above, wherein said microorganism is Escherichia coli. It is another aspect of the present invention to provide a microorganism having an ability to convert inosinic acid into 5'-guanylic acid, which has been modified so that inosinic acid dehydrogenase activity and 5'-guanylic acid synthetase activity are enhanced by increasing expression of guaB gene and guaA gene, and has been further modified so that ushA gene, aphA gene and nagD gene do not function normally. It is another aspect of the present invention to provide the microorganism as described above, which has been further modified so that one or more genes selected from purR gene, add gene and purA gene do not function normally. It is another aspect of the present invention to provide the microorganism as described above, which is selected from the group consisting of bacteria belonging to the Enterobacteriaceae family, Bacillus bacteria and Coryneform bacteria It is another aspect of the present invention to provide the microorganism as described above which is an Escherichia bacterium. It is another aspect of the present invention to provide the microorganism as described above which is an Escherichia coli. Brief Description of the Drawings [0009] [Figure 1] Figure 1 is a graph showing change in the concentration of IMP, XMP and GMP when JM109AushAAaphAApurR/pUC18-guaBA strain was reacted with IMP. [Figure 2] Figure 2 is a graph showing change in the concentration of IMP (A) and GMP (B) when JM109AushAAaphAApurR/pUC18-guaBA strain and M109AushAAaphAApurRAnagD/pUC18-guaBA strain were reacted with IMP. (Figure 3] (A) A graph showing change in the concentration of IMP and GMP when JM109AushAAaphAApurRAnagD/pUC18-guaBA strain was reacted with MP. (B) A graph showing change in the concentration of XMP and GMP when JM109AiishAAaphAApurRAriagD/pUC18-guaBAtf (Q A graph showing the accumulated amount of GMP when JM109AushAAaphAApurRAnagD/pUCl 8-guaBA strain was reacted with IMP or XMP. [Figure 4] (A) A graph showing change in the concentration of MP, XMP and GMP when MG1655AushAAaphAApurAApurRAadd/pUC18-guaBA strain was reacted with MP. (B) A graph showing the accumulated amount of GMP when MG1655AushAAaphAApurAApurRAadd/pUC18-giiaBA strain was reacted with IMP or XMP. DESCRIPTION OF THE PREFERRED EMBODIMENTS [0010] The present invention will now be described in detail. [0011] Microorganism to be used in the method of the present invention A microorganism to be used in the method of the present invention has been modified so that IMP dehydrogenate activity and GMP synthesize activity are enhanced and has an ability to convert IMP to GMP. [0012] Examples of the microorganisms include bacteria belonging to the family Enterobacteriaceae, Coryne form bacteria and Bacillus bacteria. Examples of the bacteria belonging to the family Enterobacteriaceae include Escherichia bacteria, Pantoea bacteria, Enterobacter bacteria, Klebsiella bacteria, Serratia bacteria, Erwinia bacteria, salmonella bacteria and Moragnella bacteria Escherichia bacteria are not restricted as long as they belongs to the genus Escherichia, and include Escherichia coli. Yet, specifically, ones described inNeidhardt et al. (Neidhardt, FR. C. et al., Escherichia coli and Salmonella Typhimurium, American Society for Microbiology, Washington D. C, 1208, table 1) can be used. Also, examples of Enterobacter: bacteria include Enterobacter agglomerans, Enterobacter aerogenes and the like, and examples of Pantoea bacteria include Pantoea ananatis and the like. [0013] Examples of Coryneform bacteria include bacteria classified as Coryneform bacteria according to classification known to those skilled in the art of microorganisms, bacteria which used to be classified as the genus Brevibacterium but currently re-classified as the genus Corynebacteriwn (Int J. Syst Bacteriol., 41,255 (1991)) and bacteria belonging to the genus Brevibacterium which is close to the genus Corynebacterium. Examples of such Coryneform bacteria are listed below. Corynebacterium acetoacidophUum, Corynebacterium acetoglutamicum, Corynebacterium alkanofyticum, Corynebacterium callunae, Corynebacterium glutamicum, Corynebacterium lilium, Corynebacterium melassecola, Corynebacterium therrnoaminogenes, Corynebacterium harculis, Brevibacterium divarication, Brevibacteriumfiavum, Brevibacterium immariophUum, Brevibacterium lactofermentum, Brevibacterium roseum, Brevibacterium saccharolyticum, Brevibacterium thiogenitalis, Corynebacterium ammoniagenes, Brevibacterium album, Brevibacterium cerinum, Mcrobacterium ammoniaphilum, [0014] As bacteria belonging to the genus Bacillus, bacteria classified as the genus Bacillus according to the classification known to those skilled in the art of microorganisms can be used Specific examples include, but not limited to, Bacillus subtilis, Bacillus amyloliquefaciens and the like. [0015] A method for enhancing activities of IMP dehydrogenase (a product of guaB gene) and GMP synthetase (a product of guaA gene) in the above-mentioned microorganisms will now be described. In the present invention, "modified so that the IMP dehydrogenase activity and GMP synthetase activity are enhanced" means that IMP dehydrogenase activity and GMP synthetase activity are higher than those of an unmodified strain, for example a wild type strain, of microorganisms such as bacteria belonging to the genus Escherichia [0016] IMP dehydrogenase is an enzyme catalyzing the reaction below and "IMP dehydrogenase activity" refers to an activity catalyzing a reaction generating XMP from IMP. The IMP dehydrogenase activity can be measured, for example, by the method of Gilbert (Gilbert, H. J., Lowe, C. R. and Drabble, W. T., Biochem J., 1979, Dec 1,183(3), 481-94). [0017] NAD+IMP+H20- NADH+H++*MP [0018] Also, GMP synthetase is an enzyme (EC 6.3.4.1) catalyzing the reaction below and "GMP synthetase activity" means an activity catalyzing a reaction generating GMP form XMP. [0019] ATP+XMP+NH3→AMP+pyrophosphoric acid+GMP [0020] The GMP synthetase activity can be measured, for example, by examining a decreasing rate of NADH by the method of Spector (Spector, T., Methods EnzymoL, 1978,51, p219). [0021] In order to increase IMP dehydrogenase activity and GMP synthetase activity, it is preferable to increase expression level of guaB gene and guaA gene encoding these enzymes respectively. An example of a method for increasing the expression level includes increasing the copy number of the DNA encoding IMP dehydrogenase and DNA encoding GMP synthetasein bacterial cells. In order to increase the copy number in the cells, DNA fragment each encoding IMP dehydrogenase or GMP synthetase may be linked to a vector functioning in microorganisms such as Escherichia bacteria to create a recombinant DNA, which is then introduced into a host for transformatioa The copy number ofguaB gene and guaA gene may be simultaneously or independently increased In the case of Escherichia coli, guaB gene and guaA gene form an operon (GenBank accession No. M10101), so guaBA operon may be linked to a vector to create a recombinant DNA, which is then introduced into a host for transformatioa The copy number of the genes encoding IMP dehydrogenase and GMP synthetase (guaB gene and guaA gene) increases in cells of a transformed strain, resulting in increased activities of IMP dehydrogenase and GMP synthetase. [0022] The increase in the copy number in the cells can also be attained by allowing multiple copies of IMP dehydrogenase gene and GMP synthetase gene to exist on the chromosomal DNA of the above-mentioned host Introduction of multiple copies of IMP dehydrogenase gene and GMP synthetase gene on the chromosomal DNA of bacteria belonging to the genus Escherichia can be carried out by homologous recombination by using a sequence existing on the chromosome with multiple copies as a target As the sequence existing on the chromosome with multiple copies, repetitive DNAs, inverted repeats present at the end of transposons or the like can be used. Alternatively, as disclosed in Japanese Patent Application Laid-Open Publication No. 2-109985, it is also possible that multiple copies of the desired gene can be introduced on the choromosomal DNA by integrating the desired gene on the transposon and transferring the gene. Either way, an increase in the copy number of IMP dehydrogenase gene and GMP synthetase gene in the transformant strain results in increased activities of IMP dehydrogenase and GMP synthetase. [0023] Examples of the vector for introducing the gene above include plasmid vectors such as pSTV29, pMW218 orpUC19; and phage vectors such as \ 1059, A.BF101 orM13mp9. Also, examples of the transposon include Mu, TnlO and Tn5. [0024] Since nucleotide sequences of DNAs encoding IMP dehydrogenase and GMP synthetase are known, those DNAs can be obtained by synthesizing primers based on those sequences and amplifying by PCR using the chromosomal DNA of microorganisms such as an Escherichia bacterium as a template. An example of guaA gene of Escherichia coli includes one comprising the nucleotide sequence of SEQ ID NO: 1. An example of guaB gene of Escherichia coli includes one comprising the nucleotide sequence of SEQ ID NO: 9. As for these genes, the desired DNA fragments can be selected by preparing probes based on the nucleotide sequence and carrying out hybridization from a chromosomal DNA library of Escherichia bacterium. Alternatively, the DNA fragments encoding IMP dehydrogenase and GMP synthetase may be chemically synthesized based on the known nucleotide sequences. Also, guaBA operon of Escherichia coli can be cloned using primers of SEQ ID NOs: 31 and 32. [0025] In addition, genes encoding proteins having functions equivalent to IMP dehydrogenase and GMP synthetase from microorganisms other than Escherichia bacteria may be obtained based on the above-mentioned nucleotide sequences. An example of GMP synthetase gene (guaA) of Bacillus subtUis includes one comprising the nucleotide sequence of SEQ ID NO: 3. The amino acid sequence encoded by this nucleotide sequence is shown in SEQ ID NO: 4. An example of GMP synthetase gene (guaA) of Corynebacterium glutamicum includes one comprising the nucleotide sequence shown in SEQ ID NO: 5. The amino acid sequence encoded by this nucleotide sequence is shown in SEQ ID NO: 6. An example of GMP synthetase gene (guaA) of Corynebacterium ammoniagenes includes one comprising the nucleotide sequence of SEQ ID NO: 7. The amino acid sequence encoded by this nucleotide sequence is shown in SEQ ID NO: 8. An example of IMP dehydrogenase gene (guaB) of Bacillus subtilis includes one comprising the nucleotide sequence of SEQ ID NO: 11. The amino acid sequence encoded by this nucleotide sequence is shown in SEQ ID NO: 10. An example of IMP dehydrogenase gene (guaB) of Corynebacterium glutamicum includes one comprising the nucleotide sequence of SEQ ID NO: 13. The amino acid sequence encoded by this nucleotide sequence is shown in SEQ ID NO: 14. An example of IMP dehydrogenase gene (guaB) of Corynebacterium ammoniagenes includes one cxanprising the nucleotide sequence of SEQ ID NO: 15. The amino acid sequence encoded by this nucleotide sequence is shown in SEQ ID NO: 16. Asdescribed above, since differences may exist in the nucleotide sequence of guaA gene and guaB gene by a genus, species or strain to which a microorganism belongs, guaA gene and guaB gene may be variants of the above-mentioned gene. [0026] As long as the protein encoded by guaA gene has GMP synthetase activity one having a sequence identity of not less than 80%, preferably not less than 90%, more preferably 95%, particularly preferably not less than 98% to the entire amino acid sequence of SEQIDNO:2. Also, as long as the protein encoded by guaB gene has IMP dehydrogenase activity, it may be one having a sequence identity of not less than 80%, preferably not less than 90%, more preferably 95%, particularly preferably not less than 98% to the entire amino acid sequence of SEQ ID NO: 10. The identity of amino acid sequences and of nucleotide sequences can be determined by using, for example, algorithm BLAST by Karlin and Altschul (Pro. Natl. Acad. Sci. USA, 90,5873 (1993)) or FASTA by Pearson (Methods EnzymoL, 183, 63 (1990)). Based on this algorithm BLAST, programs called BLASTN and BLASTX have been developed (See httpyAvwwjicbijilrrLnih.gov). [0027] Further, guaA gene and guaB gene to be used in the present invention are not restricted to wild type genes. As long as a functionofan encoded protein, that is, GMP synthetase activity or IMP dehydrogenase activity, is not impaired, the gene may be a mutant or artificially modified one encoding a protein comprising the amino acid sequenceofSEQIDNO:2or lObu which includes substitution, deletion, insertion, addition or inversion of one or several amino acids at one or more positions. The term, "several" varies depending on the position of the amino acid residues in a spatial structure of the protein and the type ofthearnino arid residues, and specifically means 2 to 20 amino acids, preferably 2 to 10 amino acids, more preferably 2 to 5 amino acids. The substitution is preferably a conservative substitution, and the term "conservative substitution" means mutual substitution among Phe, Tip and Tyr in cases where the substitution site has an aromatic amino acid, among Leu, lie and Val in cases where the substitution site has a hydrophobic amino acid, between Gin and Asn in cases where the substitution site has a polar amino acid, among Lys, Arg and His in cases where the substitution site has a basic amino acid, between Asp and Glu in cases where the substitution site has an acidic amino acid, and between Ser and Thr in cases where the substitution site has an amino acid having a hydroxyl group. Examples of the conservative substitution include substitution of Ala by Ser or Thr, substitution of Arg by Gin, His or Lys, substitution of Asn by Glu, Gin, Lys, His or Asp, substitution of Asp by Asn, Glu or Gin, substitution of Cys by Ser or Ala, substitution of Gin by Asn, Glu, Lys, His, Asp or Arg, substitution of Glu by Gly, Asn, Gin, Lys or Asp, substitution of Gly by Pro, substitution of His by Asn, Lys, Gin, Arg or Tyr, substitution of He by Leu, Met, Val or Phe, substitution of Leu by He, Met, Val or Phe, substitution of Lys by Asn, Glu, Gin, His or Arg, substitution of Met by lie, Leu, Val or Phe, substitution of Phe by Tip, Tyr, Met, He or Leu, substitution of Ser by Thr or Ala, substitution of Thr by Ser or Ala, substitution of Tip by Phe or Tyr, substitution of Tyr by His, Phe or Tip, and substitution of Val by Met, lie or Lea Examples of the substitution, deletion, insertion, addition, inversion or the like of amino acids as described above also include those occuiring due to natuiaUy occurring mutations (mutants and variants), such as ones based on individual differences and species differences among microorganisms having guaA gene or guaB gene. [0028] Also, guaA gene or guaB gene may be DNA capable of hybridizing with a complement of the nucleotide sequence of SEQ ID NO: 1 or 9 respectively, or with a probe which can be prepared from the sequence under stringent conditions and encaling a protein having GMP synthetase activity or IMP dehydrogenase activity. The term, "stringent conditions" herein refers to conditions under which the so-called specific hybrids form, and non-specific hybrids do not form. It is difficult to clearly express these conditions with numerical values. For example, stringent conditions include conditions under which DNAs having high identity, for instance, DNAs having an identity of not less than 80%, preferably not less than 90%, more preferably not less than 95%, particularly preferably not less than 98%, hybridize to each other, and DNAs having an identity of less than that do not hybridize to each other. Alternatively, the stringent conditions are exemplified by conditions where washing is carried out once, more preferably 2-3 times at a salt concentration and temperature corresponding to ordinary conditions of washing in Southern hybridization, i.e. 60°C, IX SSC, 0.1% SDS, preferably 0.1X SSC, 0.1% SDS, more preferably 68°C, 0.1X SSC, 0.1% SDS. [0029] Description of the above-mentioned gene variant is similarly applied to ushA gene, aphA gene, purR gene, add gene, purA gene and other genes, which are described later. [0030] Introduction of DNA into microorganisms can be carried out by the method of C. T. chung (C. T. chung et al., Proc. Natl. Acad Sci. USA, 86,2172-2175 (1989)), the method of D. M. Morrison (Methods in Enzymology, 68,326 (1979)), a method for increasing permeability of DNA by treating recipient bacterial cells with calcium chloride (Mandel, M. and Higa, A., J. Mol. BioL, 53,159 (1970)) or the like. [0031] An increase in expression level of IMP dehydrogenase gene and GMP synthetase gene can also be attained by, besides the above-mentioned gene amplification, replacing an expression regulatory sequence, such as a promoter of IMP dehydrogenase gene and GMP synthetase gene, on the chromosomal DNA or a plasmid with a stronger one. For instance, a lac promoter, a top promoter, a trcpromoter and the like are known to be a strong promoter. Also, as disclosed in WO00/18935, by introducing nucleotide substitutions of several nucleotides in a promoter region of a gene, it can be altered to a stronger one. These promoter substitutions or modification strengthen expression of IMP dehydrogenase gene and GMP synthetase gene and increase activities of both proteins. The increase in expression level ofguaB gene and guaA gene can be detected by Northern method, RT-PCR method or the like. [0032] Since expression of guaBA operon encoding IMP dehydrogenase and GMP synthetase, as well as purine operon is suppressed by PurR protein, it is preferable that purR gene (GenBank accession J04212: SEQ ID NO: 17) encoding PurR protein be modified so as not to function normally, more preferably modified to decrease its expression in bacteria to be used in the method of the present invention The modification of purR gene so that it does not function normally can be carried out by the method below. For instance, by a homologous recombination method using a gene recombination method (Experiments in Molecular Genetics, Cold Spring Harbor Laboratory press (1972); Matsuyama, S. and Mizushima, S., J. Bacterid., 162,1196 (1985)), purR gene on the chromosome can be replaced with purR gene which does not function normally (hereinafter, also referred to as "disrupted purR gene"). In homologous recombination, when a plasmid with a sequence having a homology with a sequence on the chromosome or the like is introduced into bacteria cells, the recombination takes place at the sequence having the homology at a certain frequency and the introduced plasrmd is entirely incorporated into the chromosome. Thereafter, if further recombination takes place at a site of the sequence having the homology on the chromosome, the plasmid drops. At that time, depending on a location at which the recombination takes place, the disrupted gene may be incorporated into the chromosome whereas the original normal gene may drop from the chromosome together with the plasmid By selecting such a strain, a strain in which the normal purR gene on the chromosome has been replaced with the disnqjtedrwR gene Method for Producing GMP GMP can be obtained by reacting IMP with the above-mentioned microorganism which has been modified so that IMP dehydrogenase activity and GMP synthetase activity are enhanced to convert IMP to GMP. [0042] The reaction of IMP dehydrogenase or GMP synthetase requires NAD+ or ATP, respectively. NADH generated by Ihe reaction of IMP dehydrogenase is again converted to NAD+via an oxidative phosphorylated pathway. At that time, ATP is generated. It is therefore presumed that, by simultaneously enhancing activities of IMP dehydrogenase and GMP synthetase, a reaction from IMP to GMP proceeds efficiently. In the present invention, the term, "reacting" includes to convert IMP to GMP by allowing the above-mentioned microorganism to exist in a medium to which IMP has been added and by using the microorganism as the so-called microorganism enzyme, as well as to generate GMP by adding IMP to a medium where the above-mentioned microorganism is culturing. Preferably, by adding cells of the above-mentioned microorganism after the culturing to a reaction solution containing IMP or by adding IMP to a solution containing the above-mentioned microorganism, IMP can be efficiently converted to GMP, thereby GMP is produced and accumulated [0043] As a carbon source for culturing the microorganism, any of carbohydrates such as glucose, fructose, sucrose, molasses, blackstrap molasses or starch hydrolysate; alcohols such as ethanol, glycerin or sorbitol; organic acids such as pyruvic acid, lactic acid or acetic acid; amino acids such as glycine, alanine, glutamic acid or aspartic acid can be used, as long as it can be assimilated by the above-mentioned microorganism. As a nitrogen source, various inorganic and organic ammonium salts such as ammonia, ammonia chloride, ammonium sulfate, ammonium nitrate, ammonium carbonate, ammonium acetate or ammonium phosphate; urea, various amino acids, peptone, NZ amine, meat extract, yeast extract, com steep liquor, casein hydrolysate, fish meal, digested material thereof or the like can be used. As an inorganic substance, potassium dihydrogen phosphate, potassium monophosphate, magnesium sulfate, magnesium phosphate, sodium chloride, ferrous sulfate, manganese sulfate, zinc sulfate, calcium carbonate or the like can be used. Incases where the microorganism requires specific trophic substances such as amino acids, nucleic acids or vitamins for its growth, an appropriate amount of those substances is added to the medium. The culture may be carried out in an appropriate range of pH 5.0 to 8.5 and 15°C to 45°C under aerobic condition for about 5 hours to 72 hours. In addition, for pH adjustment, an inorganic or organic, acidic or alkaline substance, as well as ammonia gas or the like can be used. [0044] The conversion from IMP to GMP can be carried out by directly injecting the culture solution of the microorganism, by injecting only microbial cells after centrifugation of the culture solution or by injecting suspension in which the bacterial cells are suspended in an appropriate solution into the reaction solution containing IMP. In the method for producing GMP of the present invention, a processed product of the above-mentioned microbial cells can also be used. Examples of the processed product of microbial cells include immobilized microbial cells in which the microbial cells are immobilized using acrylamide, carrageenan or the like. [0045] As a carbon source of the reaction solution, any of carbohydrates such as glucose, fructose, sucrose, molasses, blackstrap molasses or starch hydrolysate; alcohols such as ethanol, glycerin or sorbitol; organic acids such as pyruvic acid, lactic acid or acetic acid; amino acids such as glycine, alanine, glutamic acid or aspartic acid can be used, as long as it can be assimilated by the above-mentioned microorganisms. As a nitrogen source, various inorganic and organic ammonium salts such as ammonia, ammonia chloride, ammonium sulfate, ammonium nitrate, ammonium carbonate, ammonium acetate or ammonium phosphate; urea, various amino acids, peptone, NZ amine, meat extract, yeast extract, com steep liquor, casein hydrolysate, fish meal, digested material thereof or the like can be used. As an inorganic substance, potassium dihydrogen phosphate, potassium monophosphate, magnesium sulfate, magnesium phosphate, sodium chloride, ferrous sulfate, manganese sulfate, zinc sulfate, calcium carbonate or the like can be used. Incases where the microorganism to be used requires specific trophic substances such as amino acids, nucleic acids or vitamins for its growth, an appropriate amount of these substances is added to the medium. [0046] Further, it is preferable that permeability of nucleotide to cells be activated by adding an organic solvent to the reaction solution As the organic solvent which is an agent to activate membrane permeability of the nucleotide, xylene, toluene, benzene, fatty acid alcohol, ethyl acetate or the like can be used. It is preferable that the concentration thereof be usually used at 0.1 to 30 ml/L. The reaction may be carried out in an appropriate range of pH 5.0 to 8.5 and 15°C to 45°C under aerobic or anaerobic condition for about 1 hour to 7 days. In addition, for pH adjustment, an inorganic or organic, acidic or alkaline substance, as well as ammonia gas or the like can be used. As the raw material, IMP, one which may be chemically synthesized, commercially available or produced by a fermentation method (WO96730501, Japanese Patent Application Laid-Open Publication No. 2002-355087, Japanese Patent Application Laid-Open Publication No. 2003-325182 or the like) or the like can be used. [0047] Collection of GMP from the reaction solution can be usually carried out by combining an ion exchange resin method, a precipitation method and other known methods. [0048] [EXAMPLES] Ihe present invention will now be described more concretely by way of examples. Example 1 [0049] < 1-1 > Construction of a strain where 5'-nucleotidase encoding ushA and aphA genes are deleted from JM109 strain Construction of a strain which does not produce 5'-nucleotidase using as a parent strain Escherichia coli JM109 strain, which is commonly used as a host for DNA cloning, was first carried out 5-nucleotidase is encoded by ushA gene (Genbank Accession X03895 SEQ ID NO: 21) and aphA gene (Genbank Accession X86971 SEQ ID NO: 23). [0050] Deletion of ushA and aphA genes encoding 5'-nucleotidase was carried out by a method called "Red-driven integration" which was originally developed by Datsenko and Wanner (Proc. Natl Acad. Sci. USA, 2000, vol 97, No. 12, p6640-6645) and an excision system derived from X phage (J. BacterioL 2002 Sep; 184(18): 5200-3. Interactions between integrase and excisionase in the phage lambda excisive nucleoprotein complex. Cho EH, Gumport RL Gardner JF.). According to the "Red-driven integration" metho4 a gene disrupted strain can be constructed in one step by using a PCR product which was obtained by using, as primers, synthetic oligonucleotides designed to have part of toe desired gene in the 5'end and part of an antibiotic resistance gene in the 3' end. Further, by combining with the excision system derived from X phage, the antibiotic resistance gene incorporated in the gene distruptant strain can be removed. [0051] (1) Disruption of ushA gene As a template of PCR,a plasmidpMW118-attL-Cm-attRwas used pMWl 18-attL-Cm-attR (WO2006078039) is a plasmid in which attachment sites for X. phage, attL and attR genes as well as cat gene, which is an antibiotic resistance gene, are inserted in pMWl 18 (manufactured by Takara Bio Inc.) in the order of attL-cat-attR [0052] PCR was carried out using, as primers, synthetic oligonucleotides (SEQ ID NOs: 25 and 26) having a sequence corresponding to both ends of these attL and attR in the 3'end of the primer and a sequence corresponding to part of the desired gene, ushA,m1he 5'end of the primer. [0053] The amplified PCR product was purified on agarose gel and introduced into Esi^jerccJwa coli JM109 strain containing a plasmid pKD46 having a ternperature-sensitive replication ability by eledroporation The plasmid pKD46 (Proc. Natl. Acad. Sci. USA, 2000, vol. 97, No. 12, p6640-6645) contains a DNA fragment with a total of 2154 nucleotides of the X phage (GenBank/EMBL Accession number J02459, the 31088th nucleotide to the 33241st nucleotide) containing a gene encoding Red reconbinase (y, (3 and exo genes) of a X Red homologous recombination system controlled by a arabinose-induciblePaaB promoter. The plasmid pKD46 is required to incorporate the PCR product into the chromosome of JM109 strain. [0054] Competent cells for electroporation were prepared as follows. That is, Escherichia coli JM109 strain cultured in LB medium containing 100 mg/L of ampicillin at 30°C overnight was 100-fold diluted with 5 mL of SOB medium containing ampicillin (20 mg/L) and L-arabinose (1 mM) (Molecular Cloning: Laboratory Manual, Second Edition, Sambrook, J. et al., Cold Spring Harbor Laboratory Press (1989)). The obtained diluted cells were, while aerated, grown at 30°C until OD600 reached about 0.6. Thereafter, cells were corK«ntrated 100-fold and washed three times with 10% glycerol so as to be used for electroporation. The electroporation was carried out using 70 μ L of the obtained competent cells and about 100 ng of the PCR product Cells after the electroporation were added with 1 mL of SOC medium (Molecular Cloning: Laboratory Manual, Second Edition, Sambrook, J. et aL, Cold Spring Harbor Laboratory Press (1989)) and cultured at 37°C for 2.5 hours, followed by plate culture on L-agar medium containing Cm (Chloramphenicol) (25 mg/L) at 37°C to select Cm-resistant recombinants. Subsequently, in order to remove the pKD46 plasmid, they were subcultured twice on L-agar medium containing Cm at 42°C and ampicillin resistance of the obtained colonies was examined to obtain an ampicillin-sensitive strain in which pKD46 was cured. [0055] The deletion of ushA gene in the mutant which was able to be distinguished by a chloramphenicol resistant gene was confirmed by PCR. The obtained ushA-deleted strain was named JM109AushA::att-cat strain. [0056] Next, in order to remove att-cat gene which was introduced in ushA gene, the above-described pMW-intxis-ts was used as a helper plasmid. pMW-intxis-ts is a plasmid carrying a gene encoding integrase (Int) of the X. phage and a gene encoding excisionase (Xis), as well as having a temperature-sensitive replication ability. By the introduction of pMW-intxis-ts, attL or attR. on the chromosome is recognized, recombination take place, and die gene between attL and attR is cut out, resulting in a structure in which only attL or attR sequence remains on the chromosome. [0057] Competent cells of JM109AushA::att-cat strain obtained above were prepared in accordance with a conventional method, transformed with the helper plasmid pMW-intxis-ts, and subjected to plate culture on L-agar medium containing 50 mg/L of ampicillin at 30°C to select an ampicillin resistant strain. Next, in order to remove pMW-intxis-ts plasmid, subculture was carried out twice on L-agar medium at 42°C, ampicillin and chloramphenicol resistance of the obtained colony was examined to obtain a chloramphenicol- and ampicillin-sensitive strain where ushA is disrupted and att-cat and pMW-intxis-ts were cured. This strain was named JM109AushA. [0058] (2) Deletion ofaphA gene of JM109AushA strain Deletion ofaphA gene in JM109AushA strain was carried out according to the above method and using primers of SEQ ID NOs: 27 and 28 as primers for aphA disruption. Thereby, JM109AushAAaphA which was ushA and aphA disrupted strain was obtained [0059] <1-2 > Construction of purR gene (a gene encoding repressor of purine operon and guaBA operon) disrupted strain from JM109AushAAaphA strain Subsequently, using JM109 Δ ush Δ aph Δ strain as a parent strain, construction of a strain which does not produce a repressor of guaBA operon, PurR, was carried out PurR was encoded by purR gene (Genbank Accession J04212, SEQ ID NO: 17). The construction was carried out according to the above-described method of disruption of ushA and aphA genes and using the primers of SEQ ID NOs: 29 and 30 for purR disruption. Thereby, JM109AushAAaphAApurR was obtained. [0060] Construction of a plasmid pUC18-guaBAfor expression GMP synthetase and introduction of the plasmid into JM109AushAAaphAApurR strain The plasmid pUC 18-guaBA for expression of IMP dehydrogenase and GMP synthetase was constructed as follows. It is known that guaB and guaA genes encoding the two enzymes constitute an operon (guaBA) in Escherichia coli. Thus, PCR was carried out using primers of SEQ ID NO: 31 and SEQ ID NO: 32 to amplify guaBA operon of Escherichia coli. After the amplified fragment was purified, restriction sites formed at both ends were cleaved with SacIandKpnI. The cleaved fragment was ligatedwithpUC 18 which was also cleaved with SacI and Kpril to obtain a plasmid pUCl 8-guaBA in wrich guaBA gene was inserted This plasmid was introduced into the above-mentioned JM109AusbAAaphAApurR strain to obtain JM109AushAAaphAApurR/pUC18-guaBA strain. [0061] < 14 > Conversion from IMP to GMP using JM109AushAAaphAApurR/pUC18-guaBA strain For the above-mentioned bacterial cells, evaluation of a conversion reaction from IMP to GMP was carried out Hereinafter, a method for preparing bacterial cells, a method for reaction, composition of a reaction solution and a method of analysis for the evaluation of a conversion reaction from IMP to GMP are described. [0062] [Method for Preparing Bacterial Cells] JM109AushAAaphAApurR/pUC 18-guaBA strain was evenly spread on an LB medium plate and cultured at 37°C overnight Next day, bacterial cells corresponding to 1/32 of the plate were seeded in a 500-ml Sakaguchi flask filled with 20 ml of LB medium and cultured at 37°C overnight Bacterial cells obtained by centrifuging the culture solution of LB (600 ml) were used for a 60 ml of a reaction solution [0063] [Method for Reaction] The above-described bacterial cells from 600 ml of LB after the culturing were scraped with a medicine spoon and thereafter seeded in 60 ml of the reaction solution described later to initiate a reaction The reaction was carried out at 42°CwhilepH was maintained at 12 by adding sodium hydroxide. [0064] [Composition of Reaction Solution] 60mMIMP 50 g/L Glucose 9.2 g/L Sodium hexametaphosphate 5g/LMgS04-7H20 6.6g/L(NH4>2S04 10g/LKH2PO4 5 ml/L Xylene [0065] [Method of analysis] The reaction solution (500 ul) was sampled with time and centrifuged at 15,000 rpm for 5 minutes. The supernatant was diluted with NaOH to terminate the reaction The resulting solution was filtered and 300 μ l of the filtrate was subjected to HPLC analysis. Conditions of the analysis are as follows: Column: Two of Asahipak GS-220 (diameter 7.6 mm, 50 cm) were connected. Eluent 0.2 M NaH2P04 (pH 3.98) Temperature: 55°C Flow rate: 1 ml/min Detection: Ultraviolet (254 nm) absorption [0066] The results are shown in Figure 1. It was shown that JM109AushAAaphAApurR/ pUC18-guaBA accumulated about 16.2 g/L of GMP at maximum in the reaction solution by 12 hours of the reaction Example 2 [0067] < 2-1 > Construction of nagD gene disrupted strain from JM109AushAAaphAApurR strain Using JM109AushAAaphAApurR strain which was obtained in Example 1 < 1-2 > as a parent strain, construction of a strain which does not produce NagD was carried out NagDwas encoded by nagD gene (Genbank Accession X14135, SEQ ID NO: 41). The nagD gene disruption was carried out according to the above-described method of disruption of ushA, aphA and purR genes and using primers ofSEQIDNOs: 43 and 44 for nagD disruptioa Thereby, JM109AushAAaphAApurRAnagD was obtained [0068] <2-2 > Introduction of plasmid pUCl 8-guaBA for expression of IMP dehydrogenase and GMP synthetase into JM109AushAAaphAApurR strain and JM109AushAAaphAApurRAnagD strain The plasmid pUC 18-guaBA was introduced into the above-mentioned JM109AushAAaphAApurR strain and JM109AushAAaphAApurRAnagD strain to obtain JM109AushAAaphAApurR/pUCl 8-guaBA strain and JM109AushAAapliAApurRAnagD/pUC18-guaBA strain, respectively. [0069] < 2-3 > Conversion from IMP to GMP using JM109AushAAaphAApurR/pUCl 8-guaBA strain and JM109AusliAAaphAApurRAnagD/pUC18-guaBA strain For the above-mentioned bacterial cells, evaluation of a conversion reaction from IMP to GMP was carried out Hereinafter, a method for preparing bacterial cells, a method for reaction, composition of a reaction solution and a method of analysis for the conversion reaction from IMP to GMP are described [0070] [Method for Preparing Bacterial Cells] JM109AushAAaphAApurR/pUC18-guaBA strain or JM109AushAAaphAApurRAnagD/pUC 18-guaBA strain was evenly spread on an LB medium plate and cultured at 37°C overnight Next day, bacterial cells corresponding to 1/32 of the plate were seeded in a 500-ml Sakaguchi flask filled with 20 ml of LB medium and cultured at 37°C overnight [0071] [Method for Reaction] Thee above-described culture solution was centrifuged and bacterial cells corresponding to a dry weight of 0.8 g were seeded in 60 ml of a reaction solution to initiate a reaction. The reaction was carried out at 42°C while pH was maintained at 7.2 by adding sodium hydroxide. [0072] [Composition of Reaction Solution for Conversion Reaction from IMP to GMP] 50mMlMP 50 g/L Glucose 9.2 g/L Sodium hexametaphosphate 5g/LMgS04-7H20 6.6g/L(NH4>2S04 10g/LKH2PO4 3 ml/L Xylene [0073] [Method of Analysis] The reaction solution (500 μ l) was sampled with time and diluted with NaOH to terminate the reaction. The resulting solution was filtered and 300 μ l of the filtrate was subjected to HPLC analysis. Conditions of the analysis are as follows: Column: Two of Asahipak GS-220 (diameter 7.6 mm, 50 cm) were connected. Eluent 0.2 M NaH2P04 (pH 3.98) Temperature: 55°C Flow rate: 1 ml/min Detection: Ultraviolet (254 nm) absorption [0074] The results are shown in Figure 2. It was shown that Ml()9AushAAaphAApurR/pUC18-guaBA strain accumulated about 12.5 g/L of GMP at ^maximum in the reaction solution whereas JM109 AushAAaphAApurRAnagD/pUC 18-guaBA strain accumulated about 14.81 g/L of GMP at maximum. Example 3 [0075] Conversion from IMP to GMP and from XMP to GMP using M109AiishAAaphAApurRAnagD/pUC18-guaBA strain described in Example 2 and comparison thereof For JM109AushAAaphAApurRAnagD/pUC18-guaBA strain described in Example 2, a conversion reaction from IMP to GMP and conversion reaction from XMP to GMP were evaluated. A method for preparing bacterial cells, a method for reaction, composition of a solution for a conversion reaction from IMP to GMP and a method of analysis for the evaluation of the conversion reaction were employed in accordance with Example 2. In the conversion reaction from XMP to GMP, the same concentration of XMP, instead of IMP in the composition of the solution for the conversion reaction from IMP to GMP, was used [0076] The results are shown in Figure 3. It was shown that up to about 16.9 g/L of GMP was accumulated in the reaction solution by 4 hours of the reaction in the conversion from IMP to GMP whereas about 24.4 g/L of GMP at maximum was accumulated in the reaction solution by 7.5 hours of the reaction in the conversion from XMP to GMP, and thus the production rate of GMP in the reaction with IMP as a substrate is higher than that in the reaction with XMP as toe substrate. Example 4 [0077] < 4-1 > Construction of S'-nucleotidase encoding ushA and aphA disrupted strain from MG1655 strain Using Escherichia coli wild type MG1655 strain as a parent strain, construction of a strain which does not produce 5-nucleotidase, UshA and AphA was carried out The deletion of ushA and aphA genes encoding S'-nucleotidase was carried out by a method called "Red-driven integration" and an excision system derived from A, phage in accordance with Example 1. The produced strain was named MG1655AushAAaphA [0078] <4-2> Construction of succinyl AMP synthse encoding MG1655 AushAAaphA strain Subsequently, using MG1655 AushAAaphA strain as a parent strain, construction of a strain which does not produce succinyl AMP synthase was carriedout SuccinylAMP synthase of £ coli was encoded by purA gene (Genbank Accession J04199, SEQ ID NO: 33). The construction was carried out according to the method of disruption of ushA, aphA and purR genes shown in Example 1 and using primers of SEQ ID NOs: 35 and 36 for purA disruption Thereby, MG1655AusbAAaphAApurA was obtained. [0079] <4-3> Construction of purR gene (a gene encoding repressor of purine operonandguaBA operon) disrupted strain from MG1655AushAAaphAApurA strain Subsequently, using MG1655 AushAAaphAApurA strain as a parent strain, construction of a strain which does not produce a repressor of guaBA operon, PurR was carried out The disruption ofpurR gene was carried out in accordance with Example 1 and using primers of SEQ ID NOs: 29 and 30 for purR discription Thereby, MG1655AushAAaphAApurAApurR was obtained. [0080] <4-4> Construction of adenosine deaminase encoding add gene disrupted strain from MG1655AushAAaphAApurR strain Subsequently, using MG1655 AushAAaphAApurAApurR strain as a parent strain, construction of a strain which does not produce adenosine deaminase was carried out Adenosine deaminase of £ coli is encoded by add gene (Genbank Accession No. M59033, SEQ ID NO: 37). The construction was carried out according to the method of disruption of ushA, aphA and purR genes shown in Example 1 and using primers ofSEQ ID NOs: 39 and 40 for add disruption Thereby, MG1655AushAAaphAApurAApurRAadd strain was obtained. [0081] <4-5> Introduction of aplasmidpUC18-guaBAfor expression of IMP dehydrogenase and GMP synthetase into MG1655AushAAaphAApurAApurRAadd strain pUC18-guaBA shown in Example 1 was introduced into the above-mentioned MG1655AushAAaphAApurAApurRAadd strain to obtain MG1655AusbAAaphAApurAApurRAadd/pUCl 8-guaBA strain [0082] <4-6> Conversion from IMP or XMP to GMP using MG1655AushAAaphAApurAApurRAadd/pUC 18-guaBA strain As for the above-mentioned bacterial cells, evaluation of a conversion reaction from IMP or XMP to GMP was carried out Hereinafter, a method for preparing bacterial cells,a method for reaction, composition of a reaction solution and a method of analysis for the evaluation of the conversion reaction are described. [0083] [Method for Preparing Bacterial Cells] MG1655AusriAAaphAApurAApurRAadd/pUC 18-guaBA strain was evenly spread on an LBmedium plate and cultured at 37°C overnight Next day, bacterial cells corresponding to 1/32 of the plate were seeded in a 500-ml Sakaguchi flask filled with 20 ml of LB medium and cultured at 37°C overnight Bacterial cells obtained by centrifuging the culture solution of LB (600 ml) were used for a 60 ml of a reaction solution. [0084] [Method for Reaction] The above-described bacterial cells from 600 ml of LB after the culturing were scraped with a medicine spoon and thereafter seeded in 60 ml of the reaction solution described later to initiate a reaction, The reaction was carried out at 42°C while pH was maintained at 72 by adding sodium hydroxide. [0085] [Composition of Reaction Solution] 50 mM IMP or 50 mM XMP 50 g/L Glucose 92 g/L Sodium hexametaphosphate 5g/LMgS04-7H20 6.6g/L(NH4)2S04 10^LKH2PO4 5 ml/L Xylene [0086] [Method of Analysis] The reaction solution (500 ul) was sampled with time and diluted with NaOH to terminate the reaction. The resulting solution was filtered and 300 ulofthe filtrate was subjected to HPLC analysis. Conditions of the analysis are as follows: Column: Two of Asahipak GS-220 (diameter 7.6 mm, 50 cm) were connected. Eluent 02 MNaH2P04 (pH 3.98) Temperature: 55°C Flow rate: 1 ml/min Detection: Ultraviolet (254 ran) absorption [0087] Hie results are shown in Figure 4. Itvv^sshoM^lhatlhepKxluctioniateofGMPinthe reaction wilh IMP as a substrate is higher than that in the reaction with XMP as the substrate. Industrial Applicability [0088] According to the present invention, GMP which is useful as seasonings, pharmaceuticals and raw materials thereof can be efficiently produced [0089] [Explanation of the Sequence Listing] SEQ ID NO: 1: Nucleotide sequence of £ coli GMP synthetase (GMPS) gene (guaA) SEQ ID NO: 2: Amino acid sequence of £ coli GMPS SEQ ID NO: 3: Nucleotide sequence of B. subtUis GMPS gene (guaA) SEQ ID NO: 4: Amino acid sequence of B. subtUis GMPS SEQ ID NO: 5: Nucleotide sequence of C glutamicum GMPS gene (guaA) SEQ ID NO: 6: Amino acid sequence of C. glutamicum GMPS SEQ ID NO: 7: Nucleotide sequence of C. ammoniagenes GMPS gene (guaA) SEQ ID NO: 8: Amino acid sequence of C. ammoniagenes GMPS SEQ ID NO: 9: Nucleotide sequence of £ coli IMP dehydrogenase (IMPDH) gene (guaB) SEQ ID NO: 10: Amino acid sequence of £ coli IMPDH SEQ ID NO: 11: Nucleotide sequence of B. subtUis IMPDH gene (guaB) SEQ ID NO: 12: Amino acid sequence of B. subtUis IMPDH SEQ ID NO: 13: Nucleotide sequence of C glutamicum IMPDH gene (guaB) SEQ ID NO: 14: Amino acid sequence of C glutamicum IMPDH SEQ ID NO: 15: Nucleotide sequence of C. ammoniagenes IMPDH gene (guaB) SEQ ID NO: 16: Amino acid sequence of C. ammoniagenes IMPDH SEQ ID NO: 17: Nucleotide sequence of £ coli purR SEQ ID NO: 18: Amino acid sequence of £ coli PurR SEQ ID NO: 19: Primer sequence for cloning of £ coli purR SEQ ID NO: 20: Primer sequence for cloning of £ coli purR SEQ ID NO: 21: Nucleotide sequence of £ coli ushA SEQ ID NO: 22: Amino acid sequence of £ coli UshA SEQ ID NO: 23: Nucleotide sequence of £ coli aphA SEQ ID NO: 24: Amino acid sequence of £ coli AphA SEQ ID NO: 25: Primer sequence for disruption of £ coli ushA gene SEQ ID NO: 26: Primer sequence for disruption of £ coli ushA gene SEQ ID NO: 27: Primer sequence for disruption of £ coli aphA gene SEQ ID NO: 28: Primer sequence for disruption of £ coli aphA gene SEQ ID NO: 29: Primer sequence for disruption of £ coli purR gene SEQ ID NO: 30: Primer sequence for disruption of £ coli purR gene SEQ ID NO: 31: Primer sequence for cloning of £ coli guaBA SEQ ID NO: 32: Primer sequence for cloning of £ coli guaBA SEQ ID NO: 33: Nucleotide sequence of £ coli purA SEQ ID NO: 34: Amino acid sequence of £ coli PurA SEQ ID NO: 35: Primer sequence for disruption of £ coli purA gene SEQ ID NO: 36: Primer sequence for disruption of £ coli purA gene SEQ ID NO: 37: Nucleotide sequence of £ coli add SEQ ID NO: 38: Amino acid sequence of £ coli Add SEQ ID NO: 39: Primer sequence for disruption of £ coli add gene SEQ ID NO: 40: Primer sequence for disruption of £ coli add gene SEQ ID NO: 41: Nucleotide sequence of £ coli nagD SEQ ID NO: 42: Amino acid sequence of £ coli NagD SEQ ID NO: 43: Primer sequence for disruption of £ coli nagD gene SEQ ID NO: 44: Primer sequence for disruption of £ coli nagD gene CLAIMS 1. A method for producing 5-guanylic acid, comprising: generating 5'-guanylic acid by reacting inosinic acid with a microorganism having an ability to convert inosinic acid into 5'-guanylic acid; and collecting 5'-guanylic acid, wherein said microorganism has been modified so that inosinic acid dehydrogenase activity and 5-guanylic acid synthetase activity are enhanced. 2. The method according to claim 1, wherein inosinic acid dehydrogenase activity and 5-guanylic acid synthetase activity are enhanced by increasing expression of guaB gene and guaA gene. 3. The method according to claim 2, wherein said guaA gene encodes a protein selected from the group consisting of: (A) A protein comprising the amino acid sequence of SEQ ID NO: 2, and (B) A protein comprising the amino acid sequence of SEQ ID NO: 2 but which includes substitution, deletion, insertion, addition or inversion of one or several amino acids, and has 5'-guanylic acid synthetase activity. 4. The method according to claim 2 or 3, wherein said guaB gene encodes a protein selected from the group consisting of. (C) A protein comprising the amino acid sequence of SEQ ID NO: 10, and (D) A protein comprising the amino acid sequence of SEQ ID NO: 10 but which includes substitution, deletion, insertion, addition or inversion of one or several amino acids, and has inosinic acid dehydrogenase activity. 5. The method according to any one of claims 1 to 4, wherein said microorganism has been further modified so that one or more genes selected from ushA gene and aphA gene do not function normally. 6. The method according to any one of claims 1 to 5, wherein said microorganism has been further modified so that one or more genes selected from purR gene, add gene and pur A gene do not function normally. 7. The method according to any one of claims 1 to 6, wherein said microorganism has been further modified so that nagD gene does not function normally. 8. The method according to any one of claims 1 to 7, wherein said microorganism is selected from the group consisting of bacteria belonging to the Enterobacteriaceae family, Bacillus bacteria and Coryneform bacteria. 9. The method according to claim 8,wherein said microorganism is an Eschrichia bacterium. 10. The method according to claim 9, wherein said microorganism is Escherichia coll 11. A microorganism having an ability to convert inosinic acid into 5'-guanylic acid, which has been modified so that inosinic acid dehydrogenase activity and 5'-guanylic acid synthetase activity are enhanced by increasing expression of guaB gene and guaA gene, and has been further modified so that ushA gene, aphA gene and nagD gene do not function normally. 12. The microorganism according to claim 11, which has been further modified so that one or more genes selected from purR gene, add gene and purA gene do not function normally. 13. The microorganism according to claim 11 or 12, which is selected from the group consisting of bacteria belonging to the Enterobacteriaceae family, Bacillus bacteria and Coryneform bacteria 14. The microorganism according to claim 13 which is an Escherichia bacterium. 15. The microorganism according to claim 14 which is an Escherichia coli.