Fig. 4.

Chromosomal alterations in RO pol1–17 strains. (A and B) WT and RO strain L26–10C containing WT or mutant alleles of POL1 were held at 22 °C or shifted to 30 °C for 2.5 h in the presence of 200 mM HU; recovered isolates were examined for changes in chromosome structure by pulsed-field gel electrophoresis. Strains are labeled as in Fig. 3. (C and D) Model for generation of chromosomal translocations in RO strains. DNA lesions within chromatids (gray and red bars) are more likely to occur within Ty1 elements (purple arrows) in RO Ty1 strains (D) relative to a WT strain (C) as they comprise a greater fraction of the RO strain genome. These lesions can either be repaired from an allelic element (Left), regenerating the original chromosome structure, or from an ectopic Ty1 sequence (Right) located intra- or inter-chromosomally and resulting in the formation of deletions, inversions, and translocations.