How two helicases work together within the TFIIH complex, a perspective from structural studies of XPB and XPD helicases
Xeroderma pigmentosum group B (XPB) and D (XPD) are two DNA helicases inside the transcription factor TFIIH complex required for both transcription and DNA repair. The importance of these helicases is underscored by the fact that mutations of XPB and XPD cause diseases with extremely high sensitivity to UV-light and high risk of cancer, premature aging, etc. This mini-review focuses on recent developments in both structural and functional characterization of these XP helicases to illustrate their distinguished biological roles within the architectural restriction of the TFIIH complex. In particular, molecular mechanisms of DNA unwinding by these helicases for promoter opening during transcription initiation and bubble-creation around the lesion during DNA repair are described based on the integration of the crystal structures of XPB and XPD helicases into the architecture of the TFIIH complex.
KeywordsXPB XPD TFIIH helicase DNA repair nucleotide excision repair transcription
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