Preferential binding of yeast Rad4 center dot Rad23 complex to damaged DNA

The yeast Rad4 and Rad23 proteins form a complex that is involved in nucleo tide excision repair (NER). Their function in this process is not known yet , but genetic data suggest that they act in an early step in NER. We have p urified an epitope-tagged Rad4.Rad23 (tRad4.Rad23) complex from yeast cells , using a clone overproducing Rad4 with a hemagglutinin-tag at its C termin us. tRad4.Rad23 complex purified by both conventional and immuno-affinity c hromatography complements the in vitro repair defect of rad4 and rad23 muta nt extracts, demonstrating that these proteins are functional in NER. Using electrophoretic mobility shift assays, we show preferential binding of the tRad4.Rad23 complex to damaged DNA in vitro. UV-irradiated, as well as N-a cetoxy-2-(acetylamino)fluorene-treated DNA, is efficiently bound by the pro tein complex. These data suggest that Rad4.Rad23 interacts with DNA damage during NER and may play a role in recognition of the damage.