Dual Activity
An entirely new perspective on CDK7 function was opened when CDK7 was identified as a subunit of transcription factor IIH (TFIIH) and shown to phosphorylate the carboxy-terminal domain (CTD) of RNA polymerase II (RNAPII). TFIIH is a multiprotein complex required not only for class II transcription but also for nucleotide-excision repair. Its associated CTD-kinase activity is considered important for the promoter-clearance step of transcription, but the precise structural consequences of the phosphorylation of the CTD remain the subject of debate. Cyclin H and MAT1 are also present in TFIIH, and it is not known what, if anything, distinguishes the TFIIH-associated form of CDK7 from the quantitatively predominant free form. Whether CDK7 really displays dual-substrate specificity remains to be further explored, but there is no question that the CDK7-cyclin H-MAT1 complex is able to phosphorylate both the T-loop of CDKs and the YSPTSPS (single-letter code for amino acids) repeats of the RNAPII CTD in vitro.
Read more about this topic: CDK7 Pathway
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