Van Delft J H, Schmidt D S, Bosch L
Department of Biochemistry, University of Leiden, The Netherlands.
J Mol Biol. 1987 Oct 20;197(4):647-57. doi: 10.1016/0022-2836(87)90471-2.
Two genes, tufA and tufB, located at 73 and 88 minutes of the Escherichia coli linkage map, code for the polypeptide chain elongation factor EF-Tu. tufB is transcribed with four upstream tRNA genes, thrU, tyrU, glyT and thrT, into a cotranscript of approximately 1800 nucleotides. Here we show that in vivo processing yields a 1320 nucleotide transcript of tufB. S1 nuclease fine mapping reveals that the processing site is located in the intergenic region at about 72 to 74 nucleotides upstream from the initiation codon of the tufB cistron. A deletion in the cloned tRNA-tufB operon, encompassing the 3' half of thrU, the complete tyrU, glyT, thrT genes and ten nucleotides of the intergenic region, causes a threefold increase of the rate of plasmid tufB transcription, a fourfold increase of plasmid-borne tufB RNA and a twofold increase of plasmid-borne EF-TuB. We conclude that the deletion has eliminated a transcription termination site probably located after the thrT gene. Termination at this site uncouples tRNA synthesis from tufB transcription.
位于大肠杆菌连锁图谱73分钟和88分钟处的两个基因tufA和tufB，编码多肽链延伸因子EF-Tu。tufB与四个上游tRNA基因thrU、tyrU、glyT和thrT一起转录成一个约1800个核苷酸的共转录本。在此我们表明，体内加工产生了一个1320个核苷酸的tufB转录本。S1核酸酶精细作图显示，加工位点位于tufB顺反子起始密码子上游约72至74个核苷酸的基因间隔区。克隆的tRNA-tufB操纵子中的一个缺失，包括thrU的3' 一半、完整的tyrU、glyT、thrT基因以及基因间隔区的十个核苷酸，导致质粒tufB转录速率增加三倍、质粒携带的tufB RNA增加四倍以及质粒携带的EF-TuB增加两倍。我们得出结论，该缺失消除了一个可能位于thrT基因之后的转录终止位点。在此位点的终止使tRNA合成与tufB转录解偶联。
