P-TEFb



P-TEFb, positive transcription elongation factor b, is the key factor regulating eukaryotic mRNA transcription at the level of elongation.

It is a cyclin dependent kinase, comprised of Cdk9 and in humans one of three cyclins, T1, T2, or K.

The kinase activity of P-TEFb is required to relieve RNA polymerase II from the negative elongation properties of DSIF and NELF and enter productive elongation resulting in mRNA production.

P-TEFb is also a required cellular cofactor for HIV-Tat and inhibition of P-TEFb blocks HIV replication.