FIG. 1.

Sectoring screen for synthetic lethals with Δmrs3 Δmrs4. (A) Strain. The parent strain 96-47 contains Δmrs3 Δmrs4 Δade2 Δade3 mutations and 2μm plasmid 17-1 with MRS4, URA3, and ADE3. This strain produces red and white sectors on YPD with low adenine. (B) Mutant selection. Following UV mutagenesis, a colony/clone called J137 that failed to sector and remained red was identified. (C) Test for plasmid dependence. The parent 96-47 and mutant J137 97-19 were exposed to fluoroorotic acid (FOA) to counterselect against the plasmid, resulting in viability of the former and nonviability of the latter. (D) Plasmid swap. Parent and mutant were transformed with plasmid 17-37 pRS318-MRS4-LEU2-CHY2, and both were rendered FOA resistant (not shown). The treatment with cycloheximide (CHX) to remove the newly introduced plasmid led to viability of the parent and nonviability of the mutant. (E) Genetics. The J137 (97-19) mutant was analyzed by crossing with a Δmrs3 Δmrs4 Δade2 Δade3 strain of the opposite mating type, 93-71. The diploid homozygous for Δmrs3 Δmrs4 but heterozygous for the dre2-137 mutation was streaked on FOA plates. The diploid was able to grow, indicating that the mutation in J137 was recessive.