Transcriptional regulator which functions as a general RNA polymerase II transcription inhibitor (PubMed:15713661, PubMed:15713662). Core component of the 7SK RNP complex: in cooperation with 7SK snRNA sequesters P-TEFb in a large inactive 7SK snRNP complex preventing RNA polymerase II phosphorylation and subsequent transcriptional elongation (PubMed:15713661, PubMed:15713662).
