Transcriptional regulator which functions as a general RNA polymerase II transcription inhibitor. 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. Homooligomer and heterooligomer with HEXIM1; probably dimeric. Core component of the 7SK RNP complex, at least composed of 7SK RNA, LARP7, MEPCE, HEXIM1 (or HEXIM2) and P-TEFb (composed of CDK9 and CCNT1/cyclin-T1). Interacts with CCNT2. The coiled-coil domain mediates oligomerization. Belongs to the HEXIM family.