Requirements for RNA polymerase II carboxyl-terminal domain for activated transcription of human retroviruses human T-cell lymphotropic virus I and HIV-1.

The carboxyl-terminal domain (CTD) of RNA polymerase (RNAP) II contains multiple repeats with a heptapeptide consensus: Tyr-Ser-Pro-Thr-Ser-Pro-Ser. It has been proposed that phosphorylation of this CTD facilitates clearance and elongation of transcription complexes initiated at the promoters. However, not all transcribed promoters require RNAP II with full-length CTD. Furthermore, different activators can promote capably the transcriptional activity of polymerase II mutants deleted in the CTD. Thus, the role of the RNAP II CTD in transcription and in response to activators remains incompletely understood. To study the role of CTD in the regulated transcription of human retroviruses human-T cell lymphotropic virus I and human immunodeficiency virus 1, we used an alpha-amanitin-resistant system developed previously (Gerber, H. P., Hagmann, M., Seipel, K., Georgiev, O., West, M. A., Litingtung, Y., Schaffner, W., and Corden, J. L. (1995) Nature 374, 660-662). We found that transcription directed by the human T-cell lymphotropic virus I activator protein Tax was strongly promoted by CTD-deficient RNA polymerase II. By contrast, the human immunodeficiency virus 1 activator Tat, which is recruited to the promoter by tethering to a nascent leader RNA, requires CTD-containing polymerase II for transcriptional activity. Biochemically, we characterized that Tat associated with a cellular CTD kinase activity, whereas Tax did not. Concordantly, we found that cellular transcription factor Sp1, which can activate CTD-deficient polymerase II with an efficiency similar to Tax, also failed to bind a CTD kinase. Taken together, these observations address mechanistic corollaries between activators with(out) a linked CTD kinase and regulated transcription by RNA polymerase II moieties with(out) a CTD.