Cloning of Saccharomyces cerevisiae DNA replication genes: isolation of the CDC8 gene and two genes that compensate for the cdc8-1 mutation.

The CDC8 gene, whose product is required for DNA replication in Saccharomyces cerevisiae, has been isolated on recombinant plasmids. The yeast vector YCp50 bearing the yeast ARS1, CEN4, and URA3 sequences, to provide for replication, stability, and selection, respectively, was used to prepare a recombinant plasmid pool containing the entire yeast genome. Plasmids capable of complementing the temperature-sensitive cdc8-1 mutation were isolated by transformation of a cdc8-1 mutant and selection for clones able to grow at the nonpermissive temperature. The entire complementing activity is carried on a 0.75-kilobase fragment, as revealed by deletion mapping. This fragment lies 1 kilobase downstream from the well-characterized sup4 gene, a gene known to be genetically linked to CDC8, thus confirming that the cloned gene corresponds to the chromosomal CDC8 gene. Two additional recombinant plasmids that complement the cdc8-1 mutation but that do not contain the 0.75-kilobase fragment or any flanking DNA were also identified in this study. These plasmids may contain genes that compensate for the lack of CDC8 gene product.