ACCUMULATION OF NUCLEIC ACID-RELATED SUBSTANCES BY MICROORGANISMS

V. ROLE OF PURINE NUCLEOSIDE PHOSPHORYLASE ON THE ACCUMULATION OF GUANOSINE BY MUTANTS OF A BACILLUS STRAIN

Abstract

Studies were made on the characteristics of guanosine-producing mutants of a Bacillus strain, GnR-44 and GnR-176, which were assumed to be deficient
in purine nucleoside-hydrolyzing activity. In a culture with GnR-44, guanosine accumulated from an initial stage and increased with culture time, while with the parental strain purine bases accumulated at first, followed by the corresponding nucleosides. From experiments with a cell-free extract, these mutants were considered to be partially deficient in the phosphorylase activity for inosine, guanosine, and xanthosine. In replacement culture with GnR-44, inosine added to the medium was converted into xanthosine and guanosine, while xanthosine and guanosine appeared to remain unchanged when they were added. From these results, it was presumed that "partially defective" purine nucleoside phosphorylase of the mutants played an important role in the accumulation of guanosine.