Catalytic activity:ATP + [DNA-directed RNA polymerase] = ADP + [DNA-directed RNA polymerase] phosphate. ,Catalytic activity:ATP + a protein = ADP + a phosphoprotein. ,Function: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 production elongation by phosphorylating the CTD (C-terminal domain) of the large subunit of RNA polymerase II (RNAP II) , SUPT5H and RDBP. The CDK9/cyclin-K complex has also a kinase activity toward CTD of RNAP II and can substitute for P-TEFb in vitro. ,similarity:Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. CDC2/CDKX subfamily. ,similarity:Contains 1 protein kinase domain. ,subunit:Associates with CCNT1/cyclin-T1 to form P-TEFb. P-TEFb forms a complex with AFF4/AF5Q31. Also associates with CCNK/cyclin-K. 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. ,tissue specificity:Ubiquitous. ,
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