Genetically Altered Repression Pattern of Purine Nucleotide Synthesizing Enzymes and Inosine Production in 8-Azaguanine Resistant Mutants of Bacillus subtilis

1. The growth of AMP deaminase [EC 3.5.4.6] negative adenine auxotrophs of Bacillus subtilis was inhibited by 20 /*g/ml of 8-azaguanine. This inhibition was reversed by addition of either inosine or guanine, while that of AMP deaminase positive strains was inhibited only at cencentrations higher than 100 /ig/ml of 8-azaguanine. The growth inhibition by 150 /ig/ml of 8-azaguanine of both AMP •deaminase negative and positive adenine auxotrophs was antagonized by guanosine but not by inosine. 2. Improved inosine producers were found at a high frequency among the mutants •derived from a parental AMP deaminase negative adenine auxotroph, which was resistant to a low concentration of 8-azaguanine. The best inosine producer yielded 15 to 17 g of inosine/liter, 50 to 70 % higher than the parent. It was found that the inhibitory effect of adenine added in excess on the inosine production was signifi-cantly weaker in the mutants than in the parental strain. 3. Activity of PRPP amidotransferase [EC 2.4.2.14], the first step enzyme of IMP synthesis of the parental strain was inhibited by AMP, 8-AzaGMP and GMP in this decreasing order. Similarly these purine nucleotides inhibited PRPP amidotransferase of the mutant. 4. The formation of PRPP amidotransferase and succino-AMP lyase [EC 4.3.2.2], both responsible for the IMP synthesis, was not repressed by adenosine in the mutant, but it was repressed by guanosine. In addition, the antagonistic effect of adenosine on the repression by guanosine of IMP dehydrogenase [EC 1.2.1.14] was not found in the mutant. 5. These results supported a single apo-repressor mechanism in the purine nuleo-tide synthesis proposed in the previous report