Figure 7.

Effects of GTF depletion on initiation and elongation. (A) Phases of Pol II initiation. TFIID is recruited by core promoter elements and/or a positioned +1 nucleosome and through interactions with other TFs. TBP-dependent promoters have the most stable recruitment due to TBP interaction with its binding motif which is likely quickly stabilized by TFIIA. TAF1-dependency relies in part on TAF1 interaction with a G-rich downstream element and a positioned +1 nucleosome. XBP- and TFIIB-dependence occurs on the least stable interactions that require rapid initiation before loss of TFIID. After TFIID recruitment, the other GTFs associate to complete the PIC which then initiates. (B) RNA polymerase II elongation control with a depiction of the effect of compensatory P-TEFb release from the 7SK snRNP. Lifetimes and elongation rates for the four phases of the transcription cycle are indicated. P-TEFb dependent phosphorylation of DSIF normally occurs during the transition into productive elongation and is reversed downstream of the CPS. Termination occurs during promoter-proximal pausing and downstream of the CPS. Reduction of productive elongation leads to compensatory release of P-TEFb from the snRNP which we hypothesize leads to enhanced phosphorylation of DSIF to both increase gene body transcription and to delay termination downstream of the CPS. Green dashed outline and arrows indicate activity of released P-TEFb.