Positive transcription elongation factor b (P-TEFb) complex (P-TEFb)

The Positive transcription elongation factor b (P-TEFb) complex is a critical regulator of eukaryotic gene expression, primarily composed of the catalytic subunit Cyclin-dependent kinase 9 (CDK9) and a regulatory cyclin partner, typically Cyclin T1 (UniProt: P50750, O60563). Its primary biological function is to stimulate the transition of RNA polymerase II from promoter-proximal pausing to productive elongation by phosphorylating the polymerase's carboxyl-terminal domain (CTD) at Ser2 and associated negative elongation factors like DSIF and NELF (PubMed: 21441914). In oncology, P-TEFb is frequently hijacked by oncogenic drivers such as MYC and MLL-rearrangements to sustain the high transcriptional demands of cancer cells, particularly for short-lived anti-apoptotic proteins like MCL-1 (PubMed: 29109393). Beyond cancer, P-TEFb is a vital host factor for HIV-1 replication, where the viral Tat protein recruits the complex to the LTR promoter to enable efficient viral transcription (Wikipedia: P-TEFb). Therapeutic targeting of P-TEFb focuses on small-molecule inhibitors of CDK9, such as Alvocidib and AZD4573, which aim to selectively disrupt the expression of oncogenic and viral genes, though clinical development must balance efficacy with the risks of systemic transcriptional inhibition (PubChem: Alvocidib).

Other names

CDK9/Cyclin T complex (UniProt: P50750)CDK9/CCNT1 complex (UniProt: O60563)Cyclin-dependent kinase 9 complex (PubMed: 11554773)

Inhibition of the kinase activity of CDK9, which prevents the phosphorylation of the RNA polymerase II C-terminal domain (CTD) at Serine 2, as well as the phosphorylation of negative elongation factors (DSIF and NELF), thereby blocking the transition from transcription initiation to productive elongation (PubMed: 21441914).