Dubois M F, Nguyen V T, Bellier S, Bensaude O
Laboratoire de Génétique Moléculaire, URA CNRS 1302, Ecole Normale Supérieure, Paris, France.
J Biol Chem. 1994 May 6;269(18):13331-6.
The RNA polymerase IIO and IIA differ by the extent of phosphorylation in the carboxyl-terminal domain (CTD) of the largest subunit. It has been proposed that the IIA form of RNA polymerase II interacts with the promoter to form a stable preinitiation complex whereas the IIO form would be generated upon entry into initiation of transcription. Phosphorylation of the CTD might be required to release the interaction between the polymerase and the promoter binding factors. In this paper, we show that in the presence of actinomycin D, the phosphorylated IIO form accumulates. In contrast, the dephosphorylated IIA form accumulates while the amount of phosphorylated IIo form decreases in cells treated with CTD-kinase inhibitors such as the nucleoside analog, 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole or the isoquinoline sulfonamide derivatives H-7* or H-8. These changes are fast and suggest a very rapid phosphate turnover on the CTD. Transcription is inhibited in intact cells by drug concentrations that are effective in altering CTD phosphorylation, although no causal relationship is established yet. These effects do not concern other cellular functions such as protein synthesis. Thus isoquinoline sulfonamide derivatives might be helpful to further dissect the role of CTD phosphorylation in transcription.
RNA聚合酶IIO和IIA在最大亚基的羧基末端结构域（CTD）的磷酸化程度上存在差异。有人提出，RNA聚合酶II的IIA形式与启动子相互作用形成稳定的预起始复合物，而IIO形式则在进入转录起始时产生。CTD的磷酸化可能是释放聚合酶与启动子结合因子之间相互作用所必需的。在本文中，我们表明在放线菌素D存在的情况下，磷酸化的IIO形式会积累。相反，在用CTD激酶抑制剂（如核苷类似物5,6-二氯-1-β-D-呋喃核糖基苯并咪唑或异喹啉磺酰胺衍生物H-7*或H-8）处理的细胞中，去磷酸化的IIA形式会积累，而磷酸化的IIo形式的量会减少。这些变化很快，表明CTD上的磷酸周转非常迅速。在完整细胞中，能有效改变CTD磷酸化的药物浓度会抑制转录，尽管尚未建立因果关系。这些作用与蛋白质合成等其他细胞功能无关。因此，异喹啉磺酰胺衍生物可能有助于进一步剖析CTD磷酸化在转录中的作用。
