GENETIC AND BIOCHEMICAL STUDIES ON 5′-NUCLEOTIDE FERMENTATION

II. REPRESSION OF ENZYME FORMATION IN PURINE NUCLEOTIDE BIOSYNTHESIS IN BACILLUS SUBTILIS AND DERIVATION OF DEREPRESSED MUTANTS

Abstract

Using mutants lacking the ability to degrade 5′-nucleotides in B. subtilis M, enzyme repression in purine nucleotide biosynthesis was investigated.
1. The formation of IMP-transformylase was repressed by AMP or GMP derivatives and the formation of IMP-dehydrogenase repressed by GMP derivatives.
2. In a mutant devoid of GMP-reductase, growth was completely inhibited by a GMP derivative and this inhibition was completely overcome by the addition of a AMP derivative.
3. Among 125 guanosine-resistant mutants derived from a GMP-reductase negative mutant, several strains were found in which the formation of IMP-transformylase was resistant to the repressive effect of purine derivatives. In these strains, the formation of IMP-dehydrogenase was still sensitive to purines.
The significance of the repression mechanisms in purine nucleotide biosynthesis was discussed.