Tj. Fu et al., Cyclin K functions as a CDK9 regulatory subunit and participates in RNA polymerase II transcription, J BIOL CHEM, 274(49), 1999, pp. 34527-34530
Important progress in the understanding of elongation control by RNA polyme
rase II (RNAPII) has come from the recent identification of the positive tr
anscription elongation factor b (P-TEFb) and the demonstration that this fa
ctor is a protein kinase that phosphorylates the carboxyl-terminal domain (
CTD) of the RNAPII largest subunit, The P-TEFb complex isolated from mammal
ian cells contains a catalytic subunit (CDK9), a cyclin subunit (cyclin T1
or cyclin T2), and additional, yet unidentified, polypeptides of unknown fu
nction, To identify additional factors involved in P-TEFb function we perfo
rmed a yeast two-hybrid screen using CDK9 as bait and found that cyclin K i
nteracts with CDK9 in vivo, Biochemical analyses indicate that cyclin K fun
ctions as a regulatory subunit of CDK9, The CDK9-cyclin K complex phosphory
lated the CTD of RNAPII and functionally substituted for P-TEFb comprised o
f CDK9 and cyclin T in in vitro transcription reactions.