Saccharomyces cerevisiae RAD2 gene: isolation, subcloning, and partial characterization.

A plasmid (pNF2000) containing a 9.7-kilobase pair DNA insert that complements the UV sensitivity of rad2-1, rad2-2, and rad2-4 mutants of Saccharomyces cerevisiae has been isolated from a yeast genomic library. Genetic analysis of strains derived by transformation of rad2 mutants with an integrating plasmid containing a 9.3-kilobase pair fragment from pNF2000 shows that the fragment integrates exclusively at the chromosomal rad2 gene. We therefore conclude that this plasmid contains the RAD2 gene. The 9.3-kilobase pair fragment was partially digested with Sau3A and cloned into a multicopy yeast vector designed for easy retrieval of Sau3A inserts. The smallest subclone that retains the RAD2 gene is 4.5 kilobase pairs. This fragment was partially digested with Sau3A and cloned into an integrating plasmid. These plasmids were isolated and integrated into a heterozygous rad2/RAD2 strain. Plasmids containing internal fragments of the RAD2 gene were identified because they yielded UV-sensitive transformants due to disruption of the RAD2 gene. Sporulation of diploids transformed with integrating plasmids containing internal fragments of RAD2 gave rise to four viable haploids per tetrad, indicating that unlike the RAD3 gene of S. cerevisiae, the RAD2 gene is not essential for the viability of haploid cells under normal growth conditions. Measurements of the RNA transcript by RNA-DNA hybridization with the internal fragment as the probe indicate a size of approximately 3.2 kilobases.