Kim Minkyu, Krogan Nevan J, Vasiljeva Lidia, Rando Oliver J, Nedea Eduard, Greenblatt Jack F, Buratowski Stephen
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA.
Nature. 2004 Nov 25;432(7016):517-22. doi: 10.1038/nature03041.
The carboxy-terminal domain (CTD) of the RNA polymerase II (RNApII) largest subunit consists of multiple heptapeptide repeats with the consensus sequence YSPTSPS. Different CTD phosphorylation patterns act as recognition sites for the binding of various messenger RNA processing factors, thereby coupling transcription and mRNA processing. Polyadenylation factors are co-transcriptionally recruited by phosphorylation of CTD serine 2 (ref. 2) and these factors are also required for transcription termination. RNApII transcribes past the poly(A) site, the RNA is cleaved by the polyadenylation machinery, and the RNA downstream of the cleavage site is degraded. Here we show that Rtt103 and the Rat1/Rai1 5' --> 3' exonuclease are localized at 3' ends of protein coding genes. In rat1-1 or rai1Delta cells, RNA 3' to polyadenylation sites is greatly stabilized and termination defects are seen at many genes. These findings support a model in which poly(A) site cleavage and subsequent degradation of the 3'-downstream RNA by Rat1 trigger transcription termination.
RNA聚合酶II（RNApII）最大亚基的羧基末端结构域（CTD）由多个具有一致序列YSPTSPS的七肽重复序列组成。不同的CTD磷酸化模式作为各种信使RNA加工因子结合的识别位点，从而将转录与mRNA加工偶联起来。聚腺苷酸化因子通过CTD丝氨酸2的磷酸化被共转录招募（参考文献2），并且这些因子对于转录终止也是必需的。RNApII转录越过聚腺苷酸化位点，RNA被聚腺苷酸化机制切割，切割位点下游的RNA被降解。在这里，我们表明Rtt103和Rat1/Rai1 5'→3'核酸外切酶定位于蛋白质编码基因的3'末端。在rat1-1或rai1Δ细胞中，聚腺苷酸化位点下游的RNA 3'端被极大地稳定，并且在许多基因中观察到终止缺陷。这些发现支持了一种模型，即Rat1对聚（A）位点的切割以及随后对3'-下游RNA的降解触发转录终止。
