GSE196069
Systematic mutagenesis identifies p52/Tfb2 residues required for XPB/Ssl2 function within TFIIH and genetic interactions with TFB6
TFIIH is an evolutionarily conserved complex that plays central roles in both RNA polymerase II (pol II) transcription and DNA repair. As an integral component of the pol II Pre-Initiation Complex, TFIIH regulates the activity of the pol II enzyme in numerous ways. One of the essential functions of TFIIH resides in its XPB/Ssl2 subunit. XPB/Ssl2 is an ATP-dependent DNA translocase that stimulates promoter opening prior to transcription initiation. Crosslinking-mass spectrometry and cryo-EM results have shown a conserved interaction network involving XPB/Ssl2 and the C-terminal Hub region of the p52/Tfb2 core subunit. Here, we systematically mutagenized the HubA region of Tfb2 and screened for growth phenotypes in a TFB6 deletion background in Saccharomyces cerevisiae. We identified six lethal and twelve conditional mutants. Growth phenotypes of all but three of the conditional mutants were suppressed in the presence of Tfb6, thus identifying a functional interaction between Tfb2 HubA mutants and Tfb6, a protein that dissociates Ssl2 from TFIIH. Biochemical analysis of p52/Tfb2 mutants with severe growth phenotypes revealed defects in XPB/Ssl2 association. Further characterization of these Tfb2 mutant cells revealed defects in induction of Gal genes, and reduced occupancy TFIIH and pol II at Gal gene promoters, suggesting that functional TFIIH is required for proper Pol II recruitment to PICs in vivo. Consistent with recent structural models of TFIIH, our results identify key residues in the p52/Tfb2 HubA domain that are required for stable incorporation of XPB/Ssl2 into TFIIH, and for pol II transcription. Overall design: Examination of the role mutations in the HubA region of TFb2 play in transcriptional regulation in yeast cells.