Logarithmically growing apn1/2 cells 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 DNA plug preparation. The plugs were then incubated with T7 endonuclease I as described in the Materials and Methods or in buffer only (mock-treated). The SMD was estimated in the ethidium bromide stained gel 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)”.