Abstract
Phosphorylation of the RNA polymerase II C-terminal domain (CTD) by cyclin-dependent kinases is important for productive transcription. Here we determine the crystal structure of Cdk12/CycK and analyse its requirements for substrate recognition. Active Cdk12/CycK is arranged in an open conformation similar to that of Cdk9/CycT but different from those of cell cycle kinases. Cdk12 contains a C-terminal extension that folds onto the N- and C-terminal lobes thereby contacting the ATP ribose. The interaction is mediated by an HE motif followed by a polybasic cluster that is conserved in transcriptional CDKs. Cdk12/CycK showed the highest activity on a CTD substrate prephosphorylated at position Ser7, whereas the common Lys7 substitution was not recognized. Flavopiridol is most potent towards Cdk12 but was still 10-fold more potent towards Cdk9. T-loop phosphorylation of Cdk12 required coexpression with a Cdk-activating kinase. These results suggest the regulation of Pol II elongation by a relay of transcriptionally active CTD kinases.
Highlights
Phosphorylation of the RNA polymerase II C-terminal domain (CTD) by cyclin-dependent kinases is important for productive transcription
Whereas Cdk2/Cyclin A (CycA) and Cdk4/Cyclin D (CycD) are major players involved in the regulation of the cell cycle, five kinases—Cdk[7], Cdk[8], Cdk[9], Cdk[12] and Cdk13—have been described as transcription-regulating kinases[1]
The cyclin-dependent kinases (CDKs) and their corresponding cyclins form specific complexes including the Cdk7/CycH/Mat[1] complex, which is part of the general transcription factor TFIIH, the Cdk8/ CycC kinase module of the Mediator complex, the Cdk9/CycT complex that constitutes the active form of the positive transcription elongation factor (P-TEFb) and the recently discovered metazoan kinases Cdk[12] and Cdk[13], which both associate with Cyclin K (CycK)
Summary
Phosphorylation of the RNA polymerase II C-terminal domain (CTD) by cyclin-dependent kinases is important for productive transcription. Whereas Cdk2/Cyclin A (CycA) and Cdk4/Cyclin D (CycD) are major players involved in the regulation of the cell cycle, five kinases—Cdk[7], Cdk[8], Cdk[9], Cdk[12] and Cdk13—have been described as transcription-regulating kinases[1] They phosphorylate the C-terminal domain (CTD) of RNA polymerase II (Pol II), thereby regulating different phases of the transcription cycle from transcription initiation to elongation and termination[2]. The assignment of specific serine phosphorylations in the CTD to particular CDKs remains uncertain, because different preferences were reported in different studies Other kinase substrates such as the transcription elongation factor subunit Spt[5] contribute to the complexity[20]. Cdk[7] prefers Ser[5] as a substrate in vitro, as do its orthologues, budding yeast Kin[28] and fission yeast Mcs[6]; Cdk[7], Mcs[6] and Kin[28] have been implicated in generating the pSer[7] mark[21,22,23,24]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
