FIG. 1.

LYS2 locus and deletion mapping. (A) The 4.2-kb LYS2 locus is shown as a shaded rectangle, below which the lys2ΔRV deletion allele (ΔRV) and five lys2Δ3′ alleles (Δ5-8 through ΔB-2) are shown. Deletion end points define six LYS2 subregions (A to F), to which forward mutations were mapped. (B) Typical mapping results are shown. Twelve Lys⁻ mutants were mated to each of three deletion tester strains, SJR459, SJR460, and SJR463, containing alleles ΔB-2, ΔB-22, or ΔB-6 (Table 1), which possess different lys2Δ3′ alleles as indicated in panel A. Lys⁺ colonies (“papping”) on lysine-deficient medium result from homologous recombination between the uncharacterized lys2 forward mutation and nonoverlapping deletion alleles. The specific testers that resulted in Lys⁺ recombinants when mated to mutants allowed determination of the position of the uncharacterized forward mutation in each lys2 allele. For example, mutant 2 did not form recombinants with any of the three testers (−, −, −), indicating that its mutation maps distal to nt 2048; mutant 3 produced a (+, +, −) pattern, indicating its mutation is in region D.