We describe the structure of TFIIH and its roles in pol II initiation, promoter\proximal pausing, elongation, and termination. and TFIIB (which bind opposite ends of TBP), followed by TFIIF and pol II. Like TFIIF, TFIIE interacts directly with pol II,61, 62 and TFIIE binding helps assemble and orient TFIIH through multiple protein\protein interfaces.22 As shown in Figure ?Figure5,5, TFIIH also directly contacts downstream promoter DNA, which helps anchor it in place within the PIC. Moreover, the Nogales and Cramer labs have shown that MAT1 (Tfb3 in contain a TFIIH\like complex that lacks CAK homologs,72 yet a 7\subunit core TFIIH complex forms a stable interaction with a Mediator complex.73 Promoter opening The TFIIH subunit XPB is arguably the most important for pol II transcription, as it contains an ATPase and translocase activity that enables IACS-8968 S-enantiomer ATP\dependent opening of the promoter DNA at the transcription start site.74 This opening of the DNA template is required for transcription initiation; the single\stranded template DNA can then descend into the cleft and engage the pol II active site. Moreover, promoter opening appears to represent an important regulatory stage for gene induction, at least in certain cell types or contexts.75 As shown schematically in Figure ?Figure5,5, XPB interacts with downstream DNA and uses its Rabbit Polyclonal to DGAT2L6 5\3 DNA translocase activity13, 14 to open promoter DNA, acting as a molecular wrench.76 Because upstream DNA is fixed through TBP/TFIID binding (which also bends the DNA), XPB 5’\3′ translocation along the non\template strand (or 3’\5′ translocation on the template strand) would generate torsional stress that would be relieved by opening/melting the duplex DNA around the TSS. Thus, XPB acts to reel downstream DNA into the pol II cleft.14 The translocation mechanism for XPB has been most thoroughly studied with yeast TFIIH (XPB ortholog Ssl2), and biochemical data suggest Ssl2 enables DNA translocation in the 5’\3′ direction;13 in this case, translocation on the non\template strand would open the promoter DNA. This XPB\dependent reeling of DNA into the pol II cleft also helps explain why downstream DNA is required for TFIIH\dependent stimulation of transcription PIC include the pol II CTD and Mediator;68, 83 moreover, the Hahn lab has shown that Kin28 can promote ATP\dependent (i.e. transcription\independent) dissociation of the PIC to a re\initiation\competent scaffold complex.83 Whether such Tfb3\ or Kin28\dependent mechanisms underlie the link between TFIIK and pol II TSS scanning remain to be determined. Promoter escape and promoter\proximal pausing After formation of the open complex, pol II can initiate transcription but must break contacts with the PIC, in a process called promoter escape. Pol II promoter escape occurs after generation of a 12C13 base transcript and requires structural re\organization of TFIIB.84, 85, 86 TFIIH contributes to promoter escape as well, through mechanisms involving XPB87 and CDK7\dependent phosphorylation of the pol II CTD. The CTD of the RPB1/POLR2A subunit of human pol II contains 52 heptad repeats (26 in has also connected Cdk7 activity to neuronal differentiation, suggesting ancient links to neurogenesis.174 In a mouse model study of post\mitotic neurons, He et al. observed that Cdk7 expression was increased compared with developing neurons, and that Cdk7 inhibition (with THZ1) impaired long\term memory formation, whereas short\term memory was unaffected.175 Collectively, these findings correlate CDK7 activity to neuronal development and function; however, these links likely reflect, at least in part, the key requirement for CDK7 in pol II\dependent gene expression. Memory formation requires new transcription (e.g. of immediate early genes, many of which are DNA\binding TFs), and these findings with CDK7 are reminiscent of other studies that have linked general regulators of pol II transcription to memory formation IACS-8968 S-enantiomer in mammals.176 Pathologies Associated with TFIIH Function Defects in TFIIH function are linked to developmental diseases and numerous cancers (Table 2), and TFIIH is also targeted by several IACS-8968 S-enantiomer viral pathogens. These are summarized below. Table 2 Pathologies Associated with TFIIH Core Subunits XPB, XPD, and p8 as Well as Those Associated with the CAK Subunit CDK7 assays have demonstrated that TFIIH is not required for open complex formation if the DNA template is negatively supercoiled.65 Antisense transcription (i.e. on the non\template strand, transcribing in the opposite direction) is widespread in mammalian cells213, 223 and would promote negative supercoiling at the promoter. Potentially, this could preclude XPB action during pol II transcription initiation at some genes. How does TFIIH function during DNA repair? The PH\like domain of p62 has been shown to interact with several DNA repair factors224, 225 in a process that is regulated in part by the chromatin remodeler CHD1.226 How are these interactions controlled?.