DNA extraction
Total yeast DNA was extracted as described by Guillamon et al. (24). Briefly, the cells were grown overnight in YEPD broth and harvested by centrifugation at 4000 r.p.m. for 5 min. The cells were resuspended in 500 μl of SOE buffer (1 M sorbitol, 0.1 M EDTA-pH 7.5), transferred to 1.5 ml microfuge tubes and incubated for 2 h at 37°C with 100 T Zymolyase. The lysate was centrifuged for 1 min, the pellet was resuspended in 0.5 ml of TE buffer [50 mM Tris-HCL (pH7.4), 20 mM EDTA] and 50 μl of 20% SDS was added; the mixture was then incubated for 30 min at 65°C. After the addition of 0.2 ml potassium acetate, the mixture was placed on ice for 1 h and centrifuged for 5 min. The supernatant was transferred to a fresh tube, mixed with an equal volume of 2-propanol, and incubated for 5 min at room temperature. The pellet was air-dried and dissolved in sterile distilled water.