Logarithmically growing apn1/2, apn1/2 ntg1/2 and apn1/2 ntg1/2 ogg1 were arrested in G2/M with nocodazole, treated with MMS (0.1%, 15 min) in PBS and returned to the YPDA+nocodazole medium. Cells were collected at the indicated times and processed for PFGE analysis (A). Southern blot analysis of the gel used the Chr III specific probe CHA1 (B). Resection-related PFGE-shift of linear Chr III and formation of Chr III dimers are indicated (B). The SMD was estimated in the ethidium bromide stained gel (A) by comparing the amount of DNA material in the SMD region to DNA in the small chromosomes that experienced little breakage, “SMD / Chr (I+VI).”