The RNA chain elongation rate of the λ late mRNA is unaffected by high levels of ppGpp in the absence of amino acid starvation

Abstract

In this study, the effects of high levels of guanosine tetraphosphate (ppGpp) on the decay and RNA chain elongation kinetics of the bacteriophage λ late transcript in Escherichia coli were examined in the absence of amino acid starvation. The accumulation, mRNA decay kinetics, and RNA chain elongation rate of the λ late mRNA were determined after heat induction of λcI857 lysogens in the presence of high levels of ppGpp induced from a RelAα fragment-overproducing plasmid. The accumulation kinetics and elongation rate determinations of the late mRNA were made at long times after induction to allow a new steady state of transcriptional activities under conditions of elevated intracellular levels of ppGpp. The results indicate no prolonged or significant effect on either mRNA decay or the RNA chain elongation rate of the late mRNA as a result of elevated ppGpp levels. Surprisingly, the RNA chain elongation rate determinations indicate an RNA polymerase processivity of approximately 90-100 nucleotides/s for the λ late transcript despite the presence of high levels of ppGpp. The results are discussed in terms of various models for regulation of stable and messenger RNA synthesis in E. coli.