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).
Kashanchi, F, Brady, JN, Halanski, MA, Radonovich, MF, Price, DH, Zhou, M, Peng, J
Rice, AP, Herrmann, CH
protein serine/threonine kinase activity of P-TEFb complex [nucleoplasm]
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