Fig. 1. Identification of the sdm1 mutation. (A) Growth defect of the mgs1Δ sdm1 double mutant. Tetrad analysis of a cross between mgs1Δ and sdm1. All tiny colonies were mgs1Δ sdm1 double mutant. mgs1Δ and sdm1 mutations were confirmed by Leu⁺ prototropy and UV-sensitive phenotype, respectively. (B) Phenotypes of the sdm1 mutant with respect to growth and sensitivity to MMS, HU and UV. Wild-type, mgs1Δ and sdm1 cells were serially diluted and spotted onto YPAD plates containing 0.01% MMS or 100 mM HU. For UV sensitivity, plates on which cells were spotted were irradiated and incubated at 30°C for 3 days. (C) DNA inserts that complement the MMS sensitivity of the sdm1 mutant. (D) sdm1 mutation and wild-type sequence. Sequence analysis revealed that sdm1 is an allele of RAD18; a nonsense codon substitutes for tryptophan codon 378.