STAUROSPORINE-SENSITIVE PROTEIN-PHOSPHORYLATION IS REQUIRED FOR POSTREPLICATION DNA-REPAIR IN HUMAN-CELLS

DNA repair is an important factor of stability of pro- and eukaryotic genomes which plays a central role in mutagenesis and carcinogenesis. Genetic control of nucleotide excision repair (NER) in mammalian cells is well studied, but little is known about molecular mechanisms of po streplication repair (PRR) which allows bypass of base lesions in temp late strands after DNA replication. In Saccharomyces cerevisiae PRR is controlled by the RAD6/RAD18 pathway which involves POL30 gene encodi ng proliferating cell nuclear antigen (PCNA), and in human cells PCNA is known to be closely associated with the newly replicated chromatin where PRR probably takes place. In UV-irradiated human cells distinct PCNA foci may be detected in some cells which accumulate phosphorylate d breast cancer susceptibility protein BRCA1 and another protein BARD1 . Human PCNA is also known to be phosphorylated after UV-irradiation. In this study we found that the known inhibitor of protein kinases sta urosporine supresses PRR in NER-deficient cells which is consistent wi th the view that BRCA1 and PCNA are required for PRR, We also have sho wn that the distinct PCNA foci in UV-irradiated NER-deficient cells ar e actually associated with the newly replicated chromatin, Since RAD18 protein is not essential for normal DNA replication and directly cont rols PRR in yeast, me analysed whether this protein as well as its hum an homologs (HR18A and HR18B) have common domains with BRCA1 and BARD1 , It is found that HR18A has a subregion of homology to BARD1 and HR18 A-to BRCA1. Taken together the results indicate that BRCA1 and BARD1 m ay be involved in PRR in human cells. (C) 1998 Federation of European Biochemical Societies.