Figure 4.

Regulation of RNAPII by cell/cycle CDKs in mammalian cells. (A) In M phase, Cdk1 inhibits transcription by phosphorylating RNAPII on Ser5, thereby preventing its incorporation into the PIC. Cdk1 also phosphorylates and thereby inhibits the Cdk7 subunit of TFIIH as well as multiple components of TFIID. (B) In contrast, during G1/S phase the cell-cycle CDK Cdk2 activates transcription in HIV/infected cells. Here, the Tat protein recruits Cdk7, which enhances Ser5 phosphorylation, but Tat also recruits Cdk2, which subsequently phosphorylates Ser2 to promote transcriptional elongation. For clarity, only a single heptad repeat is shown in this figure. Created with Biorender.com.