GENETIC AND BIOCHEMICAL STUDIES ON 5'-NUCLEOTIDE FERMENTATION .4. EFFECT OF GMP REDUCTASE AND PURINE ANALOGUE RESISTANCE ON PURINE NUCLEOSIDE ACCUMULATION PATTERN IN ADENINE AUXOTROPHS OF BACILLUS SUBTILIS

1. The presence or absence of GMP reductase had no effect on nucleoside production in adenine-requiring mutants of Bacillus subtilis K, which produced a large amount of inosine when cultured in an adenine-limited medium. 2. Mutants resistant to 8-azaxanthine were derived from strain 38-3, a GMP reductase-positive inosine producer, and from strain 30-12, a GMP reductase-negative inosine producer. About 60% of the resistant mutants from strain 38-3 were found to produce xanthosine as well as inosine, while 70% of the resistant mutants from strain 30-12 produced guanosine as well as inosine. Loss of the adenine requirement in these 8-azaxanthine-resistant mutants reduced the accumulation of xanthosine or guanosine and completely halted the accumulation of inosine. Many more mutants with an altered nucleoside accumulation pattern were obtained when 8-azaxanthine was used as a selective agent than when 8-azaguanine was used. 3. Guanine-requiring mutants, GU-16 and 308-18, were isolated respectively from an 8-azaxanthine-sensitive inosine producer and from an 8-azaxanthine-resistant xanthosine-inosine producer, and the effects of guanosine on xanthosine and inosine formation were compared in these two guanine auxotrophs; strain GU-16 produced a large amount of xanthosine only when grown in media containing limited amounts of guanosine, and the production was sharply reduced by higher amounts of guanosine. In strain 308-18, however, xanthosine formation was not so greatly affected by exogenous guanosine as in strain GU-16. There was no difference in the effect of guanosine on the total amount of purine nucleosides produced, including both xanthosine and inosine, in these two strains. © 1969, Applied Microbiology, Molecular and Cellular Biosciences Research Foundation. All rights reserved.