By phosphorylating elongation factors and the C-terminal domain of RNA polymerase II, the
positive transcription elongation factor b (P-TEFb) is the critical kinase for transcription
elongation and co-transcriptional processing of eukaryotic genes. It exists in inactive small
nuclear ribonucleoprotein (7SK snRNP) and active (free P-TEFb) complexes in cells. The P-
TEFb equilibrium determines the state of cellular activation, proliferation, and differentiation.
Free P-TEFb, which is required for growth, can be recruited to RNA polymerase II via …