Microbial production of uridine. Part II. Regulation of pyrimidine nucleotide biosynthesis in cytidine deaminase-negative mutants of Bacillus subtilis.

The role of uridine and cytidine compoundsin regulating pyrimidine nucleotide biosynthesis de novo was studied with cytidine deaminase-negative mutants of Bacillus subtilis.In the wild type strain, the formation of six enzymes for uridine 5'-monophosphate (UMP)biosynthesis was severely repressed by exogenous cytidine or uracil, whereas the formation of the enzymesin a cytidine deaminase-negative mutant was repressed only by uracil.On the other hand, the formation of cytidine 5'-triphosphate (CTP) synthetase was not affected by uracil.This enzynme was repressed only when a cytidine deaminase-negative mutant was grown in the presence of excess cytidine.Studies on feedback inhibition also showed that the activity of CTP synthetase was inhibited by cytidine nucleotides, but not by uridine nucleotides.