King R A, Banik-Maiti S, Jin D J, Weisberg R A
Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institute of Health, Bethesda, Maryland 20892, USA.
Cell. 1996 Nov 29;87(5):893-903. doi: 10.1016/s0092-8674(00)81996-0.
Transcripts encoded by the cis-acting antitermination sites (put sites) of lambdoid phage HK022 promote readthrough of downstream transcription terminators. Proper conformation of the transcripts is essential for activity, since put mutations that prevent the formation of predicted RNA stems prevented antitermination, and suppressor mutations that restore the stems restored antitermination. Antitermination does not appear to require proteins other than RNA polymerase, since put-dependent readthrough of multiple sequential terminators was observed in a purified transcription system consisting of template, polymerase, substrates, and buffer. Transcription of put also increased the elongation rate of polymerase, very likely by suppressing pausing. A mutation that alters the zinc-finger region of the beta' subunit of polymerase specifically prevented the put-dependent increases in terminator readthrough and elongation rate. The simplicity of HK022 antitermination contrasts with that of other known antitermination pathways. We propose that the central effector is a transcript that directly alters the elongation properties of RNA polymerase.
类λ噬菌体HK022的顺式作用抗终止位点（put位点）编码的转录本可促进下游转录终止子的通读。转录本的正确构象对于活性至关重要，因为阻止预测RNA茎形成的put突变会阻止抗终止，而恢复茎的抑制突变则会恢复抗终止。抗终止似乎不需要RNA聚合酶以外的蛋白质，因为在由模板、聚合酶、底物和缓冲液组成的纯化转录系统中观察到了多个连续终止子的put依赖性通读。put的转录也提高了聚合酶的延伸速率，很可能是通过抑制停顿来实现的。一个改变聚合酶β'亚基锌指区域的突变特别阻止了put依赖性的终止子通读增加和延伸速率增加。HK022抗终止的简单性与其他已知抗终止途径形成对比。我们提出核心效应物是一种直接改变RNA聚合酶延伸特性的转录本。
