FIG. 3.

Adaptation is required for spontaneous and damage-induced BIR events. Haploid CDC5 rad51 and cdc5-ad rad51 strains (as in Table 1) were altered to replace the centromere-linked LEU1 gene on the control chromosome with the URA3 gene (shown as B and b::URA3, respectively). Markers A, D, E, and F represent ADE3, ARO2, LYS5, and adh4::HIS3, respectively. Control chromosome DNA is shown in outline. For spontaneous events, strains were plated on medium lacking leucine (selecting for marker B) and containing cycloheximide (selecting against CYH2). The prominent classes of rearrangements are diagrammed. For X-ray induced events, cells were plated on nonselective plates, subjected to 3 kilorads of X rays, allowed to form colonies, and replica plated on cycloheximide plates lacking leucine to screen for BIR events.