Guo H, Price D H
Department of Biochemistry, University of Iowa, Iowa City 52242.
J Biol Chem. 1993 Sep 5;268(25):18762-70.
Transcription elongation factor S-II mediates nascent transcript cleavage by RNA polymerase II (Reines, D. (1992) J. Biol. Chem. 267, 3795-3800). We have examined the mechanism of action of the Drosophila S-II analog, DmS-II, in a defined transcription system. Our results show that DmS-II is necessary and sufficient to activate nascent transcript cleavage by RNA polymerase II during transcription of a dC-tailed template. The pattern of transcripts resulting from prolonged action by DmS-II indicates that there are kinetic barriers to transcript shortening. During the cleavage reaction, the polymerase remains in register with the template strand and generates mainly nucleotide dimers. The ability of DmS-II to mediate transcript shortening resides in the carboxyl-terminal half of the protein. Our results support a model for pause suppression in which DmS-II binds to the paused polymerase, causes one cleavage event and is then released from the complex. Elongation by the polymerase then allows a second encounter with the pause site and a second chance of passing the site. Complete pause suppression may require multiple transcript shortening events for some polymerase molecules.
转录延伸因子S-II介导RNA聚合酶II引发的新生转录物切割（Reines, D. (1992) 《生物化学杂志》267, 3795 - 3800）。我们在一个明确的转录系统中研究了果蝇S-II类似物DmS-II的作用机制。我们的结果表明，在转录含dC尾模板的过程中，DmS-II对于激活RNA聚合酶II引发的新生转录物切割是必需且充分的。DmS-II长时间作用产生的转录物模式表明，转录本缩短存在动力学障碍。在切割反应过程中，聚合酶与模板链保持对齐，并主要生成核苷酸二聚体。DmS-II介导转录本缩短的能力存在于该蛋白质的羧基末端一半区域。我们的结果支持一种暂停抑制模型，即DmS-II与暂停的聚合酶结合，引发一次切割事件，然后从复合物中释放。聚合酶的延伸随后允许其再次遇到暂停位点并再次有机会通过该位点。对于某些聚合酶分子，完全的暂停抑制可能需要多次转录本缩短事件。
