GSE33128
Regulation of Mediator-dependent transcriptional activation of Pol II(G) through TFII
Pol II(G) is a novel form of RNA polymerase II that contains a tightly associated Gdown1 polypeptide. Whereas Pol II suffices for robust activator-dependent transcription in the absence of Mediator, Pol II(G) is highly dependent upon Mediator in a biochemically defined in vitro system. However, the mechanism(s) whereby Gdown1 alters the coactivator-dependence of Pol II is unknown. Here we show that Gdown1 competes with TFIIF for binding to the RPB1 and RPB5 subunits of Pol II in vitro, resulting in inhibition of a critical function of TFIIF in facilitating PIC assembly. The apparent inability of Pol II(G)  to associate with TFIIF suggests that Gdown1 must be removed from Pol II for transcription initiation. However, Mediator can actually help Pol II(G) bind to the promoter prior to subsequent Mediator functions. Complementary cell-based analyses reveal that Pol II(G) is recruited to promoter regions of subsets of actively transcribed genes, where Pol II(G) appears to modulate transcription. Our findings indicate that differential regulation of subsets of genes by Pol II and Pol II(G) occurs through the regulation of TFIIF and consequent alterations in Mediator requirements. Overall design: Genome-wide localization of PolII and Gdown1 in human IMR90 fibroblast cells using ChIP-seq