Acetylation of conserved lysines in the catalytic core of CDK9 inhibits kinase activity and regulates transcription

Molecular Biology Laboratory, Scuola Normale Superiore, AREA della Ricerca, Via Moruzzi 1, Pisa, Italy; Molecular Medicine Laboratory, International Centre for Genetic Engineering and Biotechnology (ICGEB), Padriciano 99, Trieste, Italy; On leave of absence from the Department of Biomedicine, Faculty of Medicine, University of Trieste, Italy

^* To whom correspondence should be addressed. Email: giacca{at}icgeb.org.

	Abstract

Promoter clearance and transcriptional processivity in eukaryotic cells are fundamentally regulated by the phosphorylation of the carboxy-terminal domain of RNA polymerase II (RNAPII). One of the kinases that essentially performs this function is P-TEFb (positive transcription elongation factor b), which is composed of the cyclin-dependent kinase 9 (CDK9) associated with members of the Cyclin T family. Here we show that the cellular GCN5 and P/CAF members of the GNAT family of histone acetyl-transferases regulate CDK9 function by specifically acetylating the catalytic core of the enzyme and, in particular, a lysine that is essential for ATP coordination and phosphotransfer reaction. Acetylation markedly reduces both kinase function and transcriptional activity of P-TEFb. In contrast to unmodified CDK9, the acetylated fraction of the enzyme is specifically found in the insoluble nuclear matrix compartment. Acetylated CDK9 associates with the transcriptionally silent HIV-1 provirus; upon transcriptional activation, it is substituted by the unmodified form that is involved in the elongating phase of transcription marked by Ser2-phosphorylated-RNAPII. Given the conservation of the CDK9 acetylated residues in the catalytic task of virtually all CDK proteins, we anticipate that this mechanism of regulation might play a broader role in controlling the function of other members of this kinase family.