Multi-omics and Biochemical Reconstitution Reveal CDK7-dependent Mechanisms Controlling RNA Polymerase II Function at Gene 5'- and 3'-Ends

CDK7 regulates RNA polymerase II (RNAPII) initiation, elongation, and termination through incompletely understood mechanisms. Because contaminating kinases precluded CDK7 analysis with nuclear extracts, we completed biochemical assays with purified factors. Reconstitution of RNAPII transcription initiation showed CDK7 inhibition slowed and/or paused RNAPII promoter-proximal transcription, which reduced re-initiation. These CDK7-regulatory functions were Mediator- and TFIID-dependent. Similarly in human cells, CDK7 inhibition reduced transcription by suppressing RNAPII activity at promoters, consistent with reduced initiation and/or re-initiation. Moreover, widespread 3'-end readthrough transcription was observed in CDK7-inhibited cells; mechanistically, this occurred through rapid nuclear depletion of RNAPII elongation and termination factors, including high-confidence CDK7 targets. Collectively, these results define how CDK7 governs RNAPII function at gene 5'-ends and 3'-ends, and reveal that nuclear abundance of elongation and termination factors is kinase-dependent. Because 3'-readthrough transcription is commonly induced during stress, our results further suggest regulated suppression of CDK7 activity may enable this RNAPII transcriptional response.