RAD4 gene of Saccharomyces cerevisiae: molecular cloning and partial characterization of a gene that is inactivated in Escherichia coli.

Abstract

In contrast to other Saccharomyces cerevisiae RAD genes involved in nucleotide excision repair of DNA, the RAD4 gene could not be isolated by screening a yeast genomic library for recombinant plasmids which complement the UV sensitivity of rad4 mutants (Pure et al., J. Mol. Biol. 183:31-42, 1985). We therefore attempted to walk to RAD4 from the neighboring SPT2 gene and obtained an integrating derivative of a plasmid isolated by Roeder et al. (Mol. Cell. Biol. 5:1543-1553, 1985) which contains a 4-kilobase fragment of yeast DNA including a mutant allele of SPT2. When integrated into several different rad4 mutant strains, this plasmid (pR169) complements UV sensitivity at a frequency of approximately 10%. However, a centromeric plasmid containing rescued sequences which include flanking yeast DNA no longer complements the phenotype of rad4 mutants. Complementing activity was restored by in vivo repair of a defined gap in the centromeric plasmid. The repaired plasmid fully complements the UV sensitivity of all rad4 mutants tested when isolated directly from yeast cells, but when this plasmid is propagated in Escherichia coli complementing activity is lost. We have mapped the physical location of the RAD4 gene by insertional mutagenesis and by transcript mapping. The gene is approximately 2.3 kilobases in size and is located immediately upstream of the SPT2 gene. Both genes are transcribed in the same direction. RAD4 is not an essential gene, and no increased transcription of this gene is observed in cells exposed to the DNA-damaging agent 4-nitroquinoline-1-oxide. The site of inactivation of RAD4 in a particular plasmid propagated in E. coli was localized to a 100-base-pair region by gene disruption and gap repair experiments. In addition, we have identified the approximate locations of the chromosomal rad4-2, rad4-3, and rad4-4 mutations.