Novel functional interactions between nucleotide excision DNA repair proteins influencing the enzymatic activities of TFIIH, XPG, and ERCC1-XPF

The multisubunit basal transcription factor III-I (TFIIH) has a dual involv ement in nucleotide excision repair (NER) of a variety of DNA lesions, incl uding UV-induced photoproducts, and RNA polymerase II transcription, In bot h processes, TFIIH is implicated with local DNA unwinding, which is attribu ted to its helicase subunits XPB and XPD. To further define the role of TFI IH in NER, functional interactions between TFIIH and other DNA repair prote ins were analyzed. We show that the TFIIH-associated ATPase activity is sti mulated by both XPA and the XPC-HR23B complex. However, while XPA promotes the ATPase activity specifically in the presence of damaged DNA, stimulatio n by XPC-HR23B is lesion independent. Furthermore, we reveal that TFIIH inh ibits the structure-specific endonuclease activities of both XPG and ERCC1- XPF, responsible for the 3 ' and 5 ' incision in NER, respectively. The inh ibition occurs in the absence of ATP and is reversed upon addition of ATP, These results point toward additional roles for TFIIH and ATP during NER di stinct from a requirement for DNA unwinding in the regulation of the endonu clease activities of XPG and ERCC1-XPF.