Cyclin T1–cyclin-dependent kinase 9 complex (Cyclin T1–CDK9)

Cyclin T1–cyclin-dependent kinase 9 complex (Cyclin T1–CDK9), also known as positive transcription elongation factor b (P-TEFb), is a heterodimeric protein complex combining the regulatory subunit cyclin T1 and the catalytic subunit CDK9. This complex is a key regulator of transcriptional elongation in eukaryotic cells, functioning primarily by phosphorylating the C-terminal domain of RNA polymerase II, thereby enabling efficient mRNA synthesis[1][3][4][5][6]. Cyclin T1–CDK9 is also hijacked by HIV-1 Tat protein to enhance viral gene transcription, making it especially relevant for antiviral drug development[2][5]. The complex is implicated in cancer, inflammation, and cardiac pathologies due to its role in controlling transcriptional programs and cell cycle progression. Multiple small-molecule inhibitors and experimental drugs target CDK9 activity to modulate these disease processes[1][6]. The complex is structurally characterized by a rigid cyclin box fold in Cyclin T1 and a bilobal kinase domain in CDK9, with their interaction crucial for kinase activation and substrate recognition[1][3][4].

Other names

Positive transcription elongation factor b (P-TEFb)CDK9–cyclin T1CycT1–CDK9TAK/P-TEFb complex

Inhibitors block CDK9 kinase activity, leading to decreased phosphorylation of RNA polymerase II, arresting transcription elongation[1][6] Some drugs disrupt the interaction of the complex with viral proteins, impairing HIV replication[2][5]