RAD3 gene of Saccharomyces cerevisiae: nucleotide sequence of wild-type and mutant alleles, transcript mapping, and aspects of gene regulation.

We determined the complete nucleotide sequence of the RAD3 gene of Saccharomyces cerevisiae. The coding region of the gene contained 2,334 base pairs that could encode a protein with a calculated molecular weight of 89,796. Analysis of RAD3 mRNA by Northern blots and by S1 nuclease mapping indicated that the transcript was approximately 2.5 kilobases and did not contain intervening sequences. Fusions between the RAD3 gene and the lac'Z gene of Escherichia coli were constructed and used to demonstrate that the RAD3 gene was not inducible by DNA damage caused by UV radiation or 4-nitroquinoline-1-oxide. Two UV-sensitive chromosomal mutant alleles of RAD3, rad3-1 and rad3-2, were rescued by gap repair of a centromeric plasmid, and their sequences were determined. The rad3-1 mutation changed a glutamic acid to lysine, and the rad3-2 mutation changed a glycine to arginine. Previous studies have shown that disruption of the RAD3 gene results in loss of an essential function and is associated with inviability of haploid cells. In the present experiments, plasmids carrying the rad3-1 and rad3-2 mutations were introduced into haploid cells containing a disrupted RAD3 gene. These plasmids expressed the essential function of RAD3 but not its DNA repair function. A 74-base-pair deletion at the 3' end of the RAD3 coding region or a fusion of this deletion to the E. coli lac'Z gene did not affect either function of RAD3.