Ultrastructural changes in zygote formation and autoradiographic study of DNA replication during conjugation in Saccharomyces cerevisiae.

The following stages of mating reaction were analysed in electron micrographs: initial contact of the conjugating cells, formation of a tube-like structure between the mating partners, nuclear fusion and formation of first diploid bud. Nuclear fusion was observed to take place within the conjugation tube, the fusion nucleus, however, was often localised in one of the initial conjugants. The stage of fusion nucleus, preceding the first diploid bud formation, is of longest duration in the mating process. The second longest stage is the formation of a tube-like structure. The whole conjugation process lasts at 25 degrees approximately 60 min. According to the autoradiographic data, DNA synthesis begins after nucelar fusion and proceeds during formation of the first diploid bud.