Ms. Zhou et al., TFIIH inhibits CDK9 phosphorylation during human immunodeficiency virus type 1 transcription, J BIOL CHEM, 276(48), 2001, pp. 44633-44640
Tat stimulates human immunodeficiency virus, type 1 (HIV-1), transcription
elongation by recruitment of the human transcription elongation factor P-TE
Fb, consisting of CDK9 and cyclin T1, to the TAR RNA structure. It has been
demonstrated further that CDK9 phosphorylation is required for high affini
ty binding of Tat/P-TEFb to the TAR RNA structure and that the state of P-T
EFb phosphorylation may regulate Tat transactivation. We now demonstrate th
at CDK9 phosphorylation is uniquely regulated in the HIV-1 preinitiation an
d elongation complexes. The presence of TFIIH in the HIV-1 preinitiation co
mplex inhibits CDK9 phosphorylation. As TFIIH is released from the elongati
on complex between +14 and +36, CDK9 phosphorylation is observed. In contra
st to the activity in the "soluble" complex, phosphorylation of CDK9 is inc
reased by the presence of Tat in the transcription complexes. Consistent wi
th these observations, we have demonstrated that purified TFIIH directly in
hibits CDK9 autophosphorylation. By using recombinant TFIIH subcomplexes, o
ur results suggest that the XPB subunit of TFIIH is responsible for this in
hibition of CDK9 phosphorylation. Interestingly, our results further sugges
t that the phosphorylated form of CDK9 is the active kinase for RNA polymer
ase II carboxyl-terminal domain phosphorylation.