Protein synthesis and RNA turnover in a pyrimidine-deficient bacterium

Abstract

An auxotrophic mutant of E. coli strain 15 has been isolated possessing thymine and uracil requirements. Lack of oxogenous thymine prevents DNA synthesis; lack of oxogenous uracil inhibits net RNA synthesis. Lack of both pyrimidines prevents net nucleic acid synthesis, but does not prevent protein synthesis. The protein synthesized under such conditions may be directed by induction and be a specific enzyme such as xylose isomerase. Despite the absence of net nucleic acid synthesis in pyrimidine deficiency, a fraction of the RNA was found to have a marked turnover in which preformed uracil of RNA was released and reincorporated with newly formed ribose generated in the presence of glucose- 14C. The very low isotope content of thymidine under comparable conditions indicates a negligible turnover of DNA. The possible significance of the RNA turnover has been discussed.