How to limit the speed of a motor: The intricate regulation of the XPB ATPase and Translocase in TFIIH

Abstract

The superfamily 2 helicase XPB is an integral part of the general transcription factor TFIIH and assumes essential catalytic functions in transcription initiation and nucleotide excision repair. In both processes the ATPase activity of XPB is essential. We investigated the interaction network that regulates XPB via the p52 and p8 subunits with functional mutagenesis based on a crystal structure of the full p52/p8 complex and current cryo-EM structures. Importantly, we show that XPB’s ATPase can be activated either by DNA or by the interaction with the p52/p8 proteins. Intriguingly, we observe that the ATPase activation by p52/p8 is significantly weaker than the activation by DNA and when both p52/p8 and DNA are present, p52/p8 dominates the maximum activation. We therefore define p52/p8 as the master regulator of XPB that acts as an activator and speed limiter at the same time. A correlative analysis of the ATPase and translocase activities of XPB shows that XPB only acts as a translocase within the context of complete core TFIIH and that XPA increases the processivity of the translocase complex without altering XPB’s ATPase activity. Our data unravel an intricate network that tightly controls the activity of XPB during transcription and nucleotide excision repair.

C. elegansTFIIH subunit GTF-2H5/TTDA is a non-essential transcription factor indispensable for DNA repair

“…Together with the strong UV hypersensitivity of gtf-2H5 mutants, these results indicate that GTF-2H5 is needed for efficient binding of TFIIH to damaged DNA and that in absence of GTF-2H5 repair cannot be completed. Also in vitro and in cultured mammalian cells TTDA was found to be essential for NER and the recruitment of TFIIH to sites of UV-induced DNA damage, likely by stimulating XPB ATPase activity and TFIIH translocase activity together with XPC and XPA (Theil et al , 2013; Giglia-Mari et al , 2004; Coin et al , 2006; Kappenberger et al , 2021). Our results show that GTF-2H5 has a similar, evolutionary conserved role in stimulating TFIIH activity in NER in oocytes of C. elegans.…”