Elmendorf B J, Shilatifard A, Yan Q, Conaway J W, Conaway R C
Program in Molecular and Cell Biology, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA.
J Biol Chem. 2001 Jun 22;276(25):23109-14. doi: 10.1074/jbc.M101445200. Epub 2001 Mar 19.
TFIIF, ELL, and Elongin belong to a class of RNA polymerase II transcription factors that function similarly to activate the rate of elongation by suppressing transient pausing by polymerase at many sites along DNA templates. SII is a functionally distinct RNA polymerase II elongation factor that promotes elongation by reactivating arrested polymerase. Studies of the mechanism of SII action have shown (i) that arrest of RNA polymerase II results from irreversible displacement of the 3'-end of the nascent transcript from the polymerase catalytic site and (ii) that SII reactivates arrested polymerase by inducing endonucleolytic cleavage of the nascent transcript by the polymerase catalytic site thereby creating a new transcript 3'-end that is properly aligned with the catalytic site and can be extended. SII also induces nascent transcript cleavage by paused but non-arrested RNA polymerase II elongation intermediates, leading to the proposal that pausing may result from reversible displacement of the 3'-end of nascent transcripts from the polymerase catalytic site. On the basis of evidence consistent with the model that TFIIF, ELL, and Elongin suppress pausing by preventing displacement of the 3'-end of the nascent transcript from the polymerase catalytic site, we investigated the possibility of cross-talk between SII and transcription factors TFIIF, ELL, and Elongin. These studies led to the discovery that TFIIF, ELL, and Elongin are all capable of inhibiting SII-induced nascent transcript cleavage by non-arrested RNA polymerase II elongation intermediates. Here we present these findings, which bring to light a novel activity associated with TFIIF, ELL, and Elongin and suggest that these transcription factors may expedite elongation not only by increasing the forward rate of nucleotide addition by RNA polymerase II, but also by inhibiting SII-induced nascent transcript cleavage by non-arrested RNA polymerase II elongation intermediates.
TFIIF、ELL和延伸素属于一类RNA聚合酶II转录因子，它们的功能类似，通过抑制聚合酶在DNA模板上多个位点的短暂停顿来激活延伸速率。SII是一种功能不同的RNA聚合酶II延伸因子，它通过重新激活停滞的聚合酶来促进延伸。对SII作用机制的研究表明：（i）RNA聚合酶II的停滞是由于新生转录本的3'端从聚合酶催化位点不可逆地移位所致；（ii）SII通过诱导聚合酶催化位点对新生转录本进行核酸内切酶切割来重新激活停滞的聚合酶，从而产生一个新的转录本3'端，该端与催化位点正确对齐并可延伸。SII还可诱导暂停但未停滞的RNA聚合酶II延伸中间体对新生转录本进行切割，这导致有人提出，停顿可能是由于新生转录本的3'端从聚合酶催化位点可逆性移位所致。基于与TFIIF、ELL和延伸素通过防止新生转录本的3'端从聚合酶催化位点移位来抑制停顿这一模型相符的证据，我们研究了SII与转录因子TFIIF、ELL和延伸素之间相互作用的可能性。这些研究发现，TFIIF、ELL和延伸素均能够抑制SII诱导的非停滞RNA聚合酶II延伸中间体对新生转录本的切割。在此我们展示这些发现，这些发现揭示了与TFIIF、ELL和延伸素相关的一种新活性，并表明这些转录因子可能不仅通过提高RNA聚合酶II添加核苷酸的前进速率，还通过抑制SII诱导的非停滞RNA聚合酶II延伸中间体对新生转录本的切割来加快延伸。
