This domain is found at the C-terminal end of human Cyclin-T2 (CycT2) and similar animal sequences. CycT2 is the regulatory subunit of the cyclin-dependent kinase pair (CDK9/cyclin T) complex, also called positive transcription elongation factor B (P-TEFB). This domain adopts s cyclin box fold consisting of five helices and a short C-terminal helix [2].

1: Crystal structure of human cyclin K, a positive regulator of cyclin-dependent kinase 9. Baek K, Brown RS, Birrane G, Ladias JA; J Mol Biol. 2007;366:563-573. PMID:17169370

2: The structure of P-TEFb (CDK9/cyclin T1), its complex with flavopiridol and regulation by phosphorylation. Baumli S, Lolli G, Lowe ED, Troiani S, Rusconi L, Bullock AN, Debreczeni JE, Knapp S, Johnson LN; EMBO J. 2008;27:1907-1918. PMID:18566585

3: Cyclin box structure of the P-TEFb subunit cyclin T1 derived from a fusion complex with EIAV tat. Anand K, Schulte A, Fujinaga K, Scheffzek K, Geyer M; J Mol Biol. 2007;370:826-836. PMID:17540406

4: Structural insights into the cyclin T1-Tat-TAR RNA transcription activation complex from EIAV. Anand K, Schulte A, Vogel-Bachmayr K, Scheffzek K, Geyer M; Nat Struct Mol Biol. 2008;15:1287-1292. PMID:19029897

5: Crystal structure of HIV-1 Tat complexed with human P-TEFb. Tahirov TH, Babayeva ND, Varzavand K, Cooper JJ, Sedore SC, Price DH; Nature. 2010;465:747-751. PMID:20535204