Regulatory subunit of the cyclin-dependent kinase pair (CDK9/cyclin-T1) complex, also called positive transcription elongation factor B (P-TEFb), which is proposed to facilitate the transition from abortive to productive elongation by phosphorylating the CTD (carboxy-terminal domain) of the large subunit of RNA polymerase II (RNA Pol II). In case of HIV or SIV infections, binds to the transactivation domain of the viral nuclear transcriptional activator, Tat, thereby increasing Tat's affinity for the transactivating response RNA element (TAR RNA). Serves as an essential cofactor for Tat, by promoting RNA Pol II activation, allowing transcription of viral genes. Cyclin-T1 is the predominant cyclin that associates with CDK9 to form a heterodimer called P-TEFb. P-TEFb forms a complex with AFF4/AF5Q31. Interacts with the transactivation region of HIV-1, HIV-2 and SIV Tat. Component of a complex which is at least composed of HTATSF1/Tat-SF1, P-TEFb complex, RNA pol II, SUPT5H, and NCL/nucleolin. Component of the 7SK snRNP complex at least composed of P-TEFb (composed of CDK9 and CCNT1/cyclin-T1), HEXIM1, HEXIM2, BCDIN3, SART3 proteins and 7SK and U6 snRNAs. Interacts with MDFIC. Ubiquitously expressed. Belongs to the cyclin family. Cyclin C subfamily. Note: This description may include information from UniProtKB.
Protein type: Cell cycle regulation; Transcription initiation complex
Cellular Component: nucleolus; nucleoplasm; nucleus; transcription elongation factor complex b
Molecular Function: cyclin-dependent protein kinase regulator activity; DNA binding; protein binding; protein serine/threonine kinase activity; transcription factor binding
Biological Process: positive regulation of cyclin-dependent protein kinase activity; positive regulation of transcription from RNA polymerase II promoter; positive regulation of viral transcription; protein amino acid phosphorylation; regulation of cyclin-dependent protein kinase activity; RNA elongation from RNA polymerase II promoter; snRNA transcription from RNA polymerase II promoter; transcription from RNA polymerase II promoter