Fidelity of conjugation in Saccharomyces cerevisiae.

An efficient method for the production of synchronous zygotes in Saccharomyces cerevisiae is described. Cells were synchronised under defined conditions in either an a, alpha mixed culture or by incubation of each mating type in cell-free medium in which cells of the opposite mating type had been grown. Synchronised cells were allowed to fuse under defined conditions on filter membranes. This method was used to test the fidelity of conjugation in S. cerevisiae. Under conditions where cells of a or alpha mating type were in contact with up to 6 cells of each of two strains of opposite mating type, less than 1 multiple mating in 10(4) diploid matings occurred. It is concluded that is sexual conjugation in S. cerevisiae some process distinct from cell contact restricts cell fusion to paired combinations of conjugant cells.