Isolation and characterization of yeast DNA repair genes : II. Isolation of plasmids that complement the mutations...

Plasmids that complement the yeast mutations rad50-1, rad51-1, rad54-3 and rad55-3 were obtained by transforming strains that carried a leu2 marker and the particular rad mutation, with YEp13 plasmids containing near random yeast DNA inserts. Integration of these plasmids or of fragments of these plasmids was accomplished. Genetic studies using the integrants established the presence of the genes RAD51, RAD54 and RAD55 in the respective plasmids. However, a BamHI subclone of the rad50-1 complementing plasmid failed to integrate at the RAD50 locus, indicating that no homology exists between this fragment and the RAD50 gene.A BamHI fragment from the RAD54 plasmid was shown to be internal to the RAD54 gene: its integration within a wild type copy of RAD54 causes the cell to become Rad(-); its excision is X-ray inducible and restores the Rad(+) phenotype. Since cells bearing a disrupted copy of RAD54 are able to survive, we conclude that this gene is not essential.