“…Within the 10-subunit TFIIH, the DNA translocase subunit (XPB) stimulates promoter opening (Guzder et al, 1994; Lin et al, 2005) and the cyclin-dependent kinase 7 (CDK7) phosphorylates Ser5 residues of the heptapeptide repeats (Y 1 S 2 P 3 T 4 S 5 P 6 S 7 ) of the RPB1 C-terminal domain (CTD) (Feaver et al, 1994; Fisher and Morgan, 1994), the two processes required for transcription initiation. As a focal point of transcription regulation, activation of transcription initiation has been well-characterized through biochemical studies (Buratowski et al, 1989; Cortes et al, 1992; Flores et al, 1991) and was recently revealed by structural studies from our group and others (Abdella et al, 2021; Chen et al, 2021a; Chen et al, 2021b; Rengachari et al, 2021). Compared to extensive studies of positive regulation, negative regulation of transcription initiation is less understood.…”