Saccharomyces cerevisiae MATa cells arrest cell division in response to the mating pheromone, alpha factor. After some interval of time the cells resume division. It is demonstrated here that cells recover from division arrest by becoming insensitive to the alpha factor under conditions of low cell density (10(2) cells/ml) where no alpha factor destruction occurs. The time of desensitization occurs later at higher alpha factor concentrations. Using the technique of perfusion photomicroscopy developed in this study, it was found that 95% of the desensitized cells remain insensitive to the alpha factor for greater than or equal to 3 generations at the alpha factor concentration where recovery occurred. Upon recovery, cells have generation times which are similar or identical to the calculated time from the cdc28 "start" step of cell division to cell separation. Therefore, the abnormally large recovered cells behave as if they have no growth time requirement for cell division for several generations. Desensitization was found to occur asymmetrically for parent and daughter cells. While parents (cells which have budded) are insensitive to alpha factor, their daughters (cells which have never budded and which were formed from desensitized parents during continuous perfusion with alpha factor) show 54% with a delayed generation time compared to control daughter cells.
Cell Division Kinetics