The protein encoded by this gene is a member of the cyclin-dependent kinase (CDK) family. CDK family members are highly similar to the gene products of S. cerevisiae cdc28, and S. pombe cdc2, and known as important cell cycle regulators. This kinase was found to be a component of the multiprotein complex TAK/P-TEFb, which is an elongation factor for RNA polymerase II-directed transcription and functions by phosphorylating the C-terminal domain of the largest subunit of RNA polymerase II. This protein forms a complex with and is regulated by its regulatory subunit cyclin T or cyclin K. HIV-1 Tat protein was found to interact with this protein and cyclin T, which suggested a possible involvement of this protein in AIDS.
CDK9 is also known to associate with other proteins such as TRAF2, and be involved in differentiation of skeletal muscle.
^Lee DK, Duan HO, Chang C (March 2001). "Androgen receptor interacts with the positive elongation factor P-TEFb and enhances the efficiency of transcriptional elongation". J. Biol. Chem. 276 (13): 9978–84. doi:10.1074/jbc.M002285200. PMID11266437.
^ abFu TJ, Peng J, Lee G, Price DH, Flores O (December 1999). "Cyclin K functions as a CDK9 regulatory subunit and participates in RNA polymerase II transcription". J. Biol. Chem. 274 (49): 34527–30. doi:10.1074/jbc.274.49.34527. PMID10574912.
^ abDe Falco G, Bagella L, Claudio PP, De Luca A, Fu Y, Calabretta B, Sala A, Giordano A (January 2000). "Physical interaction between CDK9 and B-Myb results in suppression of B-Myb gene autoregulation". Oncogene. 19 (3): 373–9. doi:10.1038/sj.onc.1203305. PMID10656684.
^Amini S, Clavo A, Nadraga Y, Giordano A, Khalili K, Sawaya BE (August 2002). "Interplay between cdk9 and NF-kappaB factors determines the level of HIV-1 gene transcription in astrocytic cells". Oncogene. 21 (37): 5797–803. doi:10.1038/sj.onc.1205754. PMID12173051.