Cap Binding Complex (CBC) DSIF:NELF:early elongation complex HIV-1 early elongation complex with hyperphosphorylated Pol II CTD P-TEFb complex Hyperphosphorylation (Ser2) of RNA Pol II CTD by P-TEFb complex Authored: Matthews, L, Rice, AP, 2005-07-27 00:00:00 Edited: Matthews, L, 2005-07-26 23:29:22 Pubmed10866664 Pubmed7853496 Reactome Database ID Release 43167084 Reactome, http://www.reactome.org ReactomeREACT_6297 The association between Tat, TAR and P-TEFb is believed to bring the catalytic subunit of P-TEFb(Cyclin T1:Cdk9) in close proximity to Pol II where it hyperphosphorylates the CTD of Pol II (Herrmann et al., 1995; Zhou et al. 2000). In the presence of Tat, P-TEFb(Cyclin T1:CDK9) has been shown to phosphorylate serine 5 in addition to serine 2 suggesting that modification of the substrate specificity of CDK9 may play a role in the ability of Tat to promote transcriptional elongation (Zhou et al. 2000).