Functional interactions between N-terminus and C-terminus of XPC with TFIIH in Nucleotide Excision Repair

Department of Biological SciencesNucleotide excision repair (NER) is the main DNA repair pathway to remove bulky DNA lesions formed by UV light or environmental toxins. The initial step of NER is performed by XPC-RAD23B, a protein that recognizes bulky lesions in DNA. XPC recruits TFIIH to unwind DNA and to verify the presence of DNA lesions. Although the interaction between XPC and TFIIH is critical, details of the molecular mechanisms of how XPC engages TFIIH at the sites of lesions remain unknown. Previous studies have suggested that XPC interacts with p62 and XPB, two subunits of TFIIH, through the N-terminus and C-terminus of XPC, respectively. To investigate the interaction between XPC and TFIIH, we generated cell lines expressing XPC with deletions in the N-terminus or C-terminus of XPC in XPC-deficient cells. We utilized these cell lines to conduct cell survival assays to measure the UV sensitivities and local UV irradiation assays to analyze 6-4-photoproducts (6-4PPs) repair kinetics. Our studies showed that the N-terminus of XPC is more important than C-terminus of XPC for the cellular resistance to UV irradiation and for the more efficient repair of 6-4PPs, suggesting that the interaction between XPC and p62 is crucial for NER activity. Moreover, we worked on identifying a minimal XPC-TFIIH binding domains to facilitate investigation of how XPC regulates TFIIH activity in NER.ope