Involvement of human DNA polymerase kappa in nucleotide excision repair

Nucleotide excision repair is one of the major repair pathways responsible for identifying and removing lesions in the DNA double helix. In higher eukaryotes, nucleotide excision repair is a coordinated response of over 30 proteins recruited in an ordered procession with distinct roles in the recognition, removal and repair of said lesions. A key step in the completion of the repair process is the resynthesis of the excised strand using the undamaged partner as a template. DNA polymerase kappa (pol?), a member of the Y-family, has been shown to have a role in nucleotide excision repair distinct from its traditional role in translesion synthesis. Cell lines lacking pol? showed clear defects in nucleotide excision repair and increased ultraviolet light sensitivity. Building on this established work, conserved residues were identified in the C-terminus of human pol? and mutated to alanines. Under transient expression, mutations in the ubiquitin binding domains severely impaired the recruitment to sites of damage. Cell lines defective in pol? that stably expressed these mutant polymerases showed sensitivity to ultraviolet radiation following exposure; intriguingly, this defect seems confined to the global genomic repair pathway as no substantial defect in transcription-coupled repair was observed. Following on from these observations, immunoprecipitation of the polymerase and partner proteins was investigated in an attempt to identify interactions disrupted by the mutations to the ubiquitin binding domains. These experiments indicated impairment in binding to ubiquitinated PCNA in the mutants. In further work, the recruitment of wild-type human pol? was shown to be independent of the 3' incision by the nuclease XPG during the repair process, consistent with a recently proposed model for NER.