Synchronous mating in yeast.

Homogeneous a and alpha unbudded yeast cells in logarithmic phase, grown in supplemented minimal medium and isolated by zonal gradient centrifugation, are used for mating. When these cells are resuspended in aerated defined medium, highly synchronous mating rapidly occurs. Within 20 min of incubation at 30 degrees early sexual pairing is evident; extensive agglutination is observed by 60 min, and cell fusion and bud initiation in zygotes occurs after 60-140 min. Sorbitol gradient fractionation of mating mixtures taken at various times during incubation allows the isolation of zygotes or unmated cells. Zygote preparations 90-95% purified are obtained in quantities suitable for genetic and biochemical analysis. The mating procedure is predictable and reproducible.