Abnormal Metabolism of Thymidine Nucleotides and Phosphorylation of Deoxycytidine in Escherichia coli C thy- ura- Mutant

Abstract

The Escherichia coli C thy−ura− mutant (Thy A-35) shows a rate of DNA replication (or chain elongation) one-half that of the other thy−ura− mutant (Thy A-11), but RNA and protein syntheses in the Thy A-35 mutant show the same rates as those in the Thy A-11 mutant. The viable cell numbers in the Thy A-35 mutant exhibit a slightly slower rate than those in the Thy A-11 mutant. Thymidine and deoxycytidine triphosphate (dTTP and dCTP) pools in the Thy A-35 mutant increase 2–3-fold compared to those in the Thy A-11 mutant during exponential growth. As shown by Pritchard and Zaritsky [J. Bacteriol. (1973) 114, 824–837; Philos. Trans. R. Soc. Lond. B. Biol. Sci. (1974) 267, 303– 336] the reduced rate of DNA replication in the Thy A-35 mutant reduces the DNA concentration. Consequently, the differential rate of DNA synthesis in the Thy A-35 mutant is lower than that in other strains. Also, in the Thy A-35 mutant the rate of DNA replication in the culture with deoxycytidine added increases twofold compared to that in the culture without any addition, and this rate is the same as that of DNA replication in the Thy A-11 mutant. The thymidine triphosphate (dTTP) pool in the culture with deoxycytidine of the Thy A-35 mutant increases twofold compared to its value in the culture lacking deoxycytidine. It is concluded that DNA replications in both Thy A-11 and Thy A-35 mutants depend upon the intracellular dTTP pool. In vivo and in vitro the Thy A-35 mutant cells are able to phosphorylate deoxycytidine into deoxycytidine nucleotides, and have considerable deoxycytidine kinase or such enzyme which can activate the phosphorylation of deoxycytidine.