title: Catalytic activity of Cdk9 is required for nuclear co-localization of the Cdk9/cyclin T1 (P-TEFb) complex.
abstract: Cdk9 and its binding partner cyclin T1 comprise the positive elongation factor b (P-TEFb). P-TEFb phosphorylates the RNA polymerase II carboxyl-terminal-domain (CTD) allowing efficient transcription elongation. Recent studies showed that Cdk9 is a predominant nuclear protein, and here we investigated the functional requirement for nuclear localization of Cdk9. We found that the catalytic inactive kinase mutant (Cdk9dn) fails to accumulate in the nucleus showing a diffuse sub-cellular localization. In addition to the catalityc activity, nuclear localization of Cdk9 protein requires the presence of the phospho-acceptor sites at the C-terminus tail. Finally, enforced expression of wild-type cyclinT1, which enhances nuclear localization of Cdk9wt, fails to direct the Cdk9 mutants to the nucleus. Collectively, these findings implicate that nuclear localization of Cdk9 requires auto-phosphorylation of the kinase, and highlight the presence of a regulatory mechanism underlying the nuclear localization of the P-TEFb complex.
authors.affiliation: Department of Genetics, Molecular and General Biology, University of Naples, Federico II, Naples, Italy.
authors.forename: Giuliana
authors.initials: G
authors.lastname: Napolitano
authors.forename: Barbara
authors.initials: B
authors.lastname: Majello
authors.forename: Luigi
authors.initials: L
authors.lastname: Lania
mesh_terms: D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002467:Cell Nucleus / Q000378:metabolism*; D056906:Cyclin T; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells; D006801:Humans; D009154:Mutation; D010766:Phosphorylation; D042925:Positive Transcriptional Elongation Factor B; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D021381:Protein Transport; D014162:Transfection
chemical_list: C503684:CCNT1 protein, human; D056906:Cyclin T; D016213:Cyclins; D042925:Positive Transcriptional Elongation Factor B; D017346:Protein Serine-Threonine Kinases; C467969:CDK9 protein, human; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases