Nucleotide sequence of the wild-type RAD4 gene of Saccharomyces cerevisiae and characterization of mutant rad4 alleles

Shuttle plasmids carrying the wild-type RAD4 gene of Saccharomyces cerevisiae cannot be propagated in Escherichia coli (R. Fleer, W. Siede, and E.C. Friedberg, J. Bacteriol. 169:4884-4892, 1987). In order to determine the nucleotide sequence of the cloned gene, we used a plasmid carrying a mutant allele that allows plasmid propagation of E. coli. The wild-type sequence in the region of this mutation was determined from a second plasmid carrying a different mutant rad4 allele. We established the locations and characteristics of a number of spontaneously generated plasmid-borne RAD4 mutations that alleviate the toxicity of the wild-type gene in E. coli and of several mutagen-induced chromosomal mutations that inactivate the excision repair function of RAD4. These mutations are situated in very close proximity to each other, and all are expected to result in the expression of truncated polypeptides missing the carboxy-terminal one-third of the Rad4 polypeptide. This region of the gene may be important both for the toxic effect of the Rad4 protein in E. coli and for its role in DNA repair in S. cerevisiae.