Catalytic domain of Cyclin-Dependent protein Kinase 9-like Serine/Threonine Kinases
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. This subfamily is composed of CDK9 and CDK12 from higher eukaryotes, yeast BUR1, C-type plant CDKs (CdkC), and similar proteins. CDK9, BUR1, and CdkC are functionally equivalent. They act as a kinase for the C-terminal domain of RNA polymerase II and participate in regulating mutliple steps of gene expression including transcription elongation and RNA processing. CDK9 and CdkC associate with T-type cyclins while BUR1 associates with the cyclin BUR2. CDK12 is a unique CDK that contains an arginine/serine-rich (RS) domain, which is predominantly found in splicing factors. CDK12 interacts with cyclins L1 and L2, and participates in regulating transcription and alternative splicing. CDKs belong to a large family of STKs that are regulated by their cognate cyclins. Together, they are involved in the control of cell-cycle progression, transcription, and neuronal function. The CDK9-like subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.