The relationship between the spoT gene, the synthesis of stable RNA, ribosomal proteins, and the ββ′ subunits of RNA polymerase following a nutritional shiftup of Escherichia coli

Abstract

The level of ppGpp and rates of synthesis of stable RNA, ribosomal protein, and the beta and beta' subunits of RNA polymerase were measured following a nutritional shiftup in Escherichia coli strains, NF 929 (spoT+) and NF 930 (spoT-). In the spoT+ strain, ppGpp levels decreased 50% within 2 min following shiftup, and the rates of synthesis of stable RNA, ribosomal proteins, and the beta and beta' subunits of RNA polymerase increased with little or no lag. In contrast, in the spoT- strain, ppGpp levels transiently increased 40% during the first 6 min following shiftup. An inhibition in the rate of stable RNA synthesis and a delay in the increased synthesis of ribosomal proteins and beta and beta' subunits occurred concurrently with the transient increase in ppGpp. In addition, the DNA-dependent synthesis in vitro of the beta and beta' subunits of RNA polymerase was inhibited by physiological levels of ppGpp. Because of the timing and magnitude of the changes in ppGpp levels in the spoT- strain versus the timing when the new rates of stable RNA, ribosomal protein, and beta and beta' subunits synthesis are reached, it is concluded that ppGpp is not the sole element regulating the expression of these genes.