Intracellular thymidine triphosphate concentrations in wild type and in thymine requiring mutants of Escherichia coli 15 and K12.

The intraoellular concentration of thymidine triphosphate has been measured in thymine requiring mutants of Escherichia co&i K12 and E. coli 15, and compared with that in non-mutant strains using thymine, thymidine and a mixture of thymine and deoxyguenosine, in the growth medium. The data show (1) that the thymidine triphosphate concentration rises as the thymine concentration in the growth medium is increased; (2) that the triphosphate concentration in both mutant strains is always less than that in the corresponding non-mutant strains; and (3) that thymidine inhibits its own conversion to thymidine triphosphate and also de nova synthesis of the triphosphate in non-mutant strains. It is known that in thymineless mutants the replication time of the chromosome increases ~CS the concentration of thymine in the medium decreases. The data presented in this paper suggest that the replication velocity is a function of, but not determined directly by, the intracellular thymidine triphosphete concentration.