Medlin Joanne, Scurry Andrew, Taylor Alice, Zhang Fan, Peterlin B Matija, Murphy Shona
Sir William Dunn School of Pathology, Oxford, UK.
EMBO J. 2005 Dec 7;24(23):4154-65. doi: 10.1038/sj.emboj.7600876. Epub 2005 Nov 24.
Phosphorylation of Ser2 of the heptapeptide repeat of the CTD of mammalian pol II by P-TEFb is associated with productive elongation of transcription of protein-coding genes. Here, we show that the CTD of pol II transcribing the human U2 snRNA genes is phosphorylated on Ser2 in vivo and that both the CDK9 kinase and cyclin T components of P-TEFb are required for cotranscriptional recognition of the 3' box RNA 3' end processing signal. However, inhibitors of CDK9 do not affect transcription of the U2 genes, indicating that P-TEFb functions exclusively as an RNA processing factor in expression of these relatively short, intronless genes. We also show that inhibition of CDK9 does not adversely affect either transcription of an intron-less, replication-activated histone H2b gene or recognition of the histone gene-specific U7-dependent RNA 3' end formation signal. These results emphasize that the role of P-TEFb as an activator of transcription elongation can be separated from its role in RNA processing and that neither function is universally required for expression of mammalian pol II-dependent genes.
哺乳动物RNA聚合酶II（pol II）羧基末端结构域（CTD）七肽重复序列的丝氨酸2（Ser2）磷酸化与蛋白质编码基因转录的有效延伸相关。在此，我们表明，在体内转录人U2小核RNA（snRNA）基因的pol II的CTD在Ser2处发生磷酸化，并且P-TEFb的细胞周期蛋白依赖性激酶9（CDK9）激酶和细胞周期蛋白T成分都是共转录识别3'框RNA 3'末端加工信号所必需的。然而，CDK9抑制剂并不影响U2基因的转录，这表明P-TEFb在这些相对较短的、无内含子基因的表达中仅作为一种RNA加工因子发挥作用。我们还表明，抑制CDK9对无内含子的、复制激活的组蛋白H2b基因的转录或组蛋白基因特异性的、依赖于U7的RNA 3'末端形成信号的识别均无不利影响。这些结果强调，P-TEFb作为转录延伸激活剂的作用可以与其在RNA加工中的作用分开，并且这两种功能都不是哺乳动物pol II依赖性基因表达普遍必需的。
