Transcriptional activation independent of TFIIH kinase and the RNA polymerase II mediator in vivo
Transcriptional activation independent of TFIIH kinase and the RNA polymerase II mediator in vivo
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作者：
Lee, D;Lis, JT
RNA聚合酶II最大亚基的羧基末端结构域（CTD）在体内（1）和体外（2）基因转录周期的早期步骤中被蛋白激酶多次磷酸化。在酵母中，主要CTD激酶是一般转录因子TFIIH的亚基，由必需基因KIN 28编码（参考文献3）。尽管CTD及其磷酸化对转录很重要（4-6），但体外研究（7，8）质疑CTD磷酸化是否是绝对必需的步骤。已经提出了通过Kin 28的CTD磷酸化对于酵母中转录的普遍重要性，因为对于所有测试的基因，在温度敏感性kin 28突变体中，转录在非允许温度下被抑制（9，10）。然而，使用这样的突变体和铜诱导的靶向破坏方法，我们在这里表明，即使当细胞缺乏Kin 28时，某些基因的转录也可以被高度诱导。我们还表明，这些Kin 28非依赖性基因的转录不依赖于Srb 4和Srb 6，Srb 4和Srb 6是CTD相关转录介质复合物的关键组分（11）。这些结果表明，至少有两个不同的转录激活途径：一个是依赖于Kin 28和介质复合物，而另一个不是。
The carboxy-terminal domain (CTD) of the largest subunit of RNA polymerase II becomes multiply phosphorylated by protein kinases during early steps in the gene transcription cycle both in vivo(1) and in vitro(2). In yeast, the major CTD kinase is a subunit of the general transcription factor TFIIH, and is encoded by an essential gene, KIN28 (ref. 3). Although the CTD and its phosphorylation are important for transcription(4-6), in vitro studies(7,8) have challenged whether CTD phosphorylation is an absolutely required step. The general importance of CTD phosphorylation by Kin28 for transcription in yeast has been suggested because, for all genes tested, transcription is inhibited at the non-permissive temperature in temperature-sensitive kin28 mutants(9,10). However, using such a mutant and a copper-inducible targeted destruction method, we show here that transcription of certain genes can be highly induced even when cells lack Kin28. We also show that transcription of these Kin28-independent genes is independent of Srb4 and Srb6, critical components of the CTD-associated transcriptional mediator complex(11). These results indicate that there are at least two distinct pathways for transcriptional activation: one is dependent on Kin28 and the mediator complex, and the other is not.