GENETIC AND BIOCHEMICAL STUDIES ON 5′-NUCLEOTIDE FERMENTATION

III. GENETIC DEREPRESSION OF ENZYME FORMATION IN PURINE NUCLEOTIDE BIOSYNTHESIS IN BACILLUS SUBTILIS

Abstract

The genetic alteration in the mechanism of enzyme repression operating 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 10μg/ml of guanosine, were derepressed for PRPP amidotransferase, 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 100μg/ml of guanosine, could not be distinguished from their parent strains in the formation of the five 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 μg/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 200μg/ml of guanosine, was derepressed for IMP transf ormylase and sAMP lyase.
Based on these results, the genetic control of enzyme repression in purine nucleotide synthesis was discussed.