A pleiotropic mutation (cpm) which is localized in the vicinity of the spoOA gene is described in Bacillus subtilis. The mutation inhibits spore formation, rendering bacteria auxotrophic for adenine and tyrosine, enhances sensitivity to antibodiotics, decreases cell motility, inhibits the ability to grow on pentoses and to maintain bacteriophage multiplication, induces severalfold the activities of alkaline proteinase and α‐amylase. At the same time, the cpm mutant starts to excrete inosine into the growth medium. This excretion most probably is explained by 1 50‐fold increase in the activity of inosine monophosphate: 5′‐nucleotidase and a 10‐fold decrease in the activity of purine nucleoside phosphorylase. The inosine production and Ade− phenotype of the cpm mutant is not accompanied by the change in the activity of succinyl adenosine monophosphate synthetase. The nature of the mutation is discussed.

A mutant of Brevibacterium ammoniagenes producing large quantities of UMP and uracil is described. The mutations render bacteria braditrophic for arginine, sensitive to adenine, resistant to rifampicin and pyrimidine analogues 5‐fluorouracil, 5‐fluorouridine, azuuracil and thiouracil. The activities of enzymes involved in the UMP biosynthesis, i.e. orotate phosphoribosyl‐transferase, orotate‐5‐monophosphate decarboxylase, dihydroorotate oxidase, are 4‐, 3.5‐ and 4.5‐fold higher in the mutant than in the parent strain when grown in minimal medium. The synthesis of these enzymes in mutant cells is not repressed in the presence of exogenous Ura. True revertants, which completely restore the wild‐type phenotype, occur among the Arg+ clones. The nature of the mutation is discussed.

A mutant of Brevibacterium ammoniagenes producing large quantities of UMP and uracil is described. The mutations render bacteria braditrophic for arginine, sensitive to adenine, resistant to rifampicin and pyrimidine analogues 5-fluorouracil, 5-fluorouridine, azauracil and thiouracil. The activities of enzymes involved in the UMP biosynthesis, i.e. orotate phosphoribosyltransferase, orotate-5-monophosphate decarboxylase, dihydroorotate oxidase, are 4-, 3.5- and 4.5-fold higher in the mutant than in the parent strain when grown in minimal medium. The synthesis of these enzymes in mutant cells is not repressed in the presence of exogenous Ura. True revertants, which completely restore the wild-type phenotype, occur among the Arg+ clones. The nature of the mutation is discussed.