ISOLATION OF HUMAN COMPLEXES PROFICIENT IN NUCLEOTIDE EXCISION-REPAIR

More than 20 polypeptides are required for the process of nucleotide e xcision repair (NER) in both human and yeast cells, This pathway of ex cision repair has most often been viewed as an ordered multi-step proc ess involving steps of damage recognition, incision/excision and final ly repair DNA synthesis, Here we present evidence for the existence of a complex of human NER proteins pre-assembled in the absence of damag ed DNA, This multi-protein complex was initially isolated from HeLa ce ll extracts by affinity chromatography on a matrix containing the dama ge recognition protein XPA. Subsequent co-immunoprecipitation and gel filtration experiments demonstrated that a significant portion of the human NER proteins was present in the form of a high molecular weight complex and that these complexes, or repairosomes, were capable of per forming all steps of NER in vitro. Consistent with studies indicating that DNA polymerases delta and epsilon can both function in NER, these two polymerases are found in these repairosome complexes.