Protein kinase involved in the regulation of transcription (PubMed:
10574912, PubMed:
10757782, PubMed:
11145967, PubMed:
11575923, PubMed:
11809800, PubMed:
11884399, PubMed:
14701750, PubMed:
16109376, PubMed:
16109377, PubMed:
20930849, PubMed:
28426094). Member of the cyclin-dependent kinase pair (CDK9/cyclin-T) complex, also called positive transcription elongation factor b (P-TEFb), which facilitates the transition from abortive to productive elongation by phosphorylating the CTD (C-terminal domain) of the large subunit of RNA polymerase II (RNAP II) POLR2A, SUPT5H and RDBP (PubMed:
10574912, PubMed:
10757782, PubMed:
11145967, PubMed:
11575923, PubMed:
11809800, PubMed:
11884399, PubMed:
14701750, PubMed:
16109376, PubMed:
16109377, PubMed:
20930849, PubMed:
28426094). This complex is inactive when in the 7SK snRNP complex form (PubMed:
10574912, PubMed:
10757782, PubMed:
11145967, PubMed:
11575923, PubMed:
11809800, PubMed:
11884399, PubMed:
14701750, PubMed:
16109376, PubMed:
16109377, PubMed:
20930849, PubMed:
28426094). Phosphorylates EP300, MYOD1, RPB1/POLR2A and AR and the negative elongation factors DSIF and NELF (PubMed:
9857195, PubMed:
10912001, PubMed:
11112772, PubMed:
12037670, PubMed:
20081228, PubMed:
20980437, PubMed:
21127351). Regulates cytokine inducible transcription networks by facilitating promoter recognition of target transcription factors (e.g. TNF-inducible RELA/p65 activation and IL-6- inducible STAT3 signaling) (PubMed:
17956865, PubMed:
18362169). Promotes RNA synthesis in genetic programs for cell growth, differentiation and viral pathogenesis (PubMed:
10393184, PubMed:
11112772). P-TEFb is also involved in cotranscriptional histone modification, mRNA processing and mRNA export (PubMed:
15564463, PubMed:
19575011, PubMed:
19844166). Modulates a complex network of chromatin modifications including histone H2B monoubiquitination (H2Bub1), H3 lysine 4 trimethylation (H3K4me3) and H3K36me3; integrates phosphorylation during transcription with chromatin modifications to control co-transcriptional histone mRNA processing (PubMed:
15564463, PubMed:
19575011, PubMed:
19844166). The CDK9/cyclin-K complex has also a kinase activity towards CTD of RNAP II and can substitute for CDK9/cyclin-T P-TEFb in vitro (PubMed:
21127351). Replication stress response protein; the CDK9/cyclin-K complex is required for genome integrity maintenance, by promoting cell cycle recovery from replication arrest and limiting single-stranded DNA amount in response to replication stress, thus reducing the breakdown of stalled replication forks and avoiding DNA damage (PubMed:
20493174). In addition, probable function in DNA repair of isoform 2 via interaction with KU70/XRCC6 (PubMed:
20493174). Promotes cardiac myocyte enlargement (PubMed:
20081228). RPB1/POLR2A phosphorylation on 'Ser-2' in CTD activates transcription (PubMed:
21127351). AR phosphorylation modulates AR transcription factor promoter selectivity and cell growth. DSIF and NELF phosphorylation promotes transcription by inhibiting their negative effect (PubMed:
9857195, PubMed:
10912001, PubMed:
11112772). The phosphorylation of MYOD1 enhances its transcriptional activity and thus promotes muscle differentiation (PubMed:
12037670).
