The RAD1 and RAD3 genes of Saccharomyces cerevisiae are required for excision repair of UV damaged DNA. In addition, the RAD3 gene is essential since rad3 deletions are recessive lethals. We have examined the induction of the RAD1 and RAD3 genes by DNA damage and during the cell division cycle. We have made fusions of the RAD1 and RAD3 genes with the Escherichia coli lacZ gene encoding β-galactosidase. β-galactosidase activity was measured in a Rad+ yeast strain containing the RAD1-lacZ or the RAD3-lacZ fusion, either in a multicopy replicating plasmid or as a single copy integrant resulting from transformation with an integrating plasmid which transforms yeast by homologous recombination in the yeast genome. No induction of β-galactosidase activity occurred after ultraviolet light (UV) or 4-nitroquinoline-1-oxide (NQO) treatment. Haploid cells of mating type a were synchronized by treatment with α factor and β-galactosidase activity was determined during different cell cycle stages. No change in β-galactosidase activity was observed in the strain containing the RAD1-lacZ or the RAD3-lacZ fusion integrated in the yeast genome.
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