Studies on a Mutant Strain of Escherichia coli which Requires both Methionine and Lysine in place of the Pyrimidine Moiety of Thiamine for Growth

Abstract

A mutant strain of Escherichia coli. D-30, requiring the pyrimidine moiety of thiamine (OMP) for both aerobic and anaerobic growth in a minimal medium supplemented with the thiazole moiety of thiamine (Th) was isolated from mutant 26-43, requiring Th. The requirement for OMP could be replaced by methionine and lysine, but not by succinate. The mutant could not grow in the minimal medium supplemented with 1 nM OMP, but the rapid growth was observed by the addition of methionine. The growth in the minimal medium Supplemented with methionine and lysine was strongly inhibited by adenosine. The growth of mutant 26-43 in the minimal medium supplemented with Th was also considerably inhibited by adenosine. This inhibition was restored by the addition of both methionine and lysine. A mutant strain, 6-60, isolated from a Th-requiring mutant (26-43), required OMP and adenosine for growth. The requirement for OMP in mutant 6-60 was substituted by methionine and lysine as found in mutant D-30. The formation of OMP by cell suspension of mutant D-30 was shown to be dependent on the presence of methioninc. This formation by cell suspensions of mutants D-30, 26-43 and 6-60 was shown to be activated by the presence of methionine and lysine. These results suggest that the OMP synthesis in mutant D-30 was not completely blocked. Possible mechanisms for the activation of the OMP biosynthesis by methionine and lysine are discussed.