GENETIC AND BIOCHEMICAL STUDIES ON 5′-NUCLEOTIDE FERMENTATION

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Abstract
The genetic alteration in the mechanism of enzyme repression in the purine nucleotide synthesis of B. subtilis was investigated, using the mutants resistant to various concentrations of guanosine derived from strain G-6, a guanine-requiring mutant of GMP reductase-negative strain, TF-11. Strains 1-40 and 3-8 which were derived from G-6 as mutants resistant to 10 [mu]g/ml of guanosine, were derepressed for 5-phosphoribosylpy-rophosphate (PRPP) amidotransferase, inosine monophosphate (IMP) transformylase and IMP dehydrogenase. Adenylosuccinate lyase and adenylosuccinate synthetase were still repressed in these strains. Strains 40-15 and 8-5, which were derived from 1-40 and 3-8, respectively, as mutants resistant to 100 [mu]g/ml of guanosine, could not be distinguished from their parent strains in the formation of the 5 enzymes tested. Strains 40-57, 4015-4 and 85-1, which were derived from 1-40, 40-15, and 8-5, respectively, as mutants resistant to 1,000 [mu]g/ml of guanosine, were derepressed for sAMP lyase; sAMP synthetase was still repressed. Strain GR-40, which was directly derived from TF-11 as a mutant resistant to 200 [mu]g/ml of guanosine, was derepressed for IMP transformylase and sAMP lyase. Based on these results, the genetic control of enzyme repression in purine nucleotide synthesis was discussed.

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