Tedin K, Bläsi U
Institute for Microbiology and Genetics, The University of Vienna, Biocenter, Dr. Bohr-Gasse 9, A-1030 Vienna, Austria.
J Biol Chem. 1996 Jul 26;271(30):17675-86. doi: 10.1074/jbc.271.30.17675.
In this study, the effects of high levels of guanosine tetraphosphate (ppGpp) on the decay and RNA chain elongation kinetics of the bacteriophage lambda 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 lambda late mRNA were determined after heat induction of lambdacI857 lysogens in the presence of high levels of ppGpp induced from a RelAalpha 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 lambda 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.
在本研究中，在不存在氨基酸饥饿的情况下，检测了高水平鸟苷四磷酸（ppGpp）对大肠杆菌中噬菌体λ晚期转录本的衰变和RNA链延伸动力学的影响。在存在由RelAα片段过量表达质粒诱导产生的高水平ppGpp的情况下，对λcI857溶原菌进行热诱导后，测定了λ晚期mRNA的积累、mRNA衰变动力学和RNA链延伸速率。晚期mRNA的积累动力学和延伸速率测定是在诱导后很长时间进行的，以便在细胞内ppGpp水平升高的条件下实现转录活性的新稳态。结果表明，ppGpp水平升高对晚期mRNA的衰变或RNA链延伸速率均无延长或显著影响。令人惊讶的是，RNA链延伸速率测定表明，尽管存在高水平的ppGpp，但λ晚期转录本的RNA聚合酶持续合成能力约为90 - 100个核苷酸/秒。根据大肠杆菌中稳定RNA和信使RNA合成调控的各种模型对结果进行了讨论。
