Polyethylene glycol induced membrane fusion in yeast protoplasts.

Freeze-etching and ultrathin section techniques were used to demonstrate ultrastructural change in plasma membranes during fusion of Saccharomyces cerevisiae protoplasts. Incubation of protoplasts in 30% (w/v) polyethylene glycol fed to strong reduction in the number of particles in areas of close membrane contact and disappearance of invaginations. On sections, neighbouring plasma membranes merged to pentalaminar or trilaminar structures. After incubation in regeneration medium, these membrane changes progressed to form rounded bulging areas with crater-like openings which are thought to be channels through which coalescence of partner's cytoplasms may occur.