(6a) rat1-1 and rai1 mutants are not sensitive to MMS. WT (KRY105), rtt103 (KRY230) WT RAI1 (KRY631), rai1 (KRY632), WT RAT1 (KRY633) and rat1-1 (KRY634) strains were grown to mid-log phase. 5 µl of 10-fold serial dilutions of yeast cultures were plated on YPD plates containing MMS and incubated at 30°C for 2–3 days. (6b) rai1 mutants are not sensitive to HO endonuclease. WT (KRY622), rtt103 (KRY646), rai1 (KRY624), were induced with galactose for HO endonuclease to produce DSBs. The percentage survival on galactose compared to WT was calculated from three independent experiments and error bars denote SD.