AN EXTRACELLULAR MEIOSIS-PROMOTING FACTOR IN SACCHAROMYCES-CEREVISIAE

Meiosis and sporulation in the yeast Saccharomyces cerevisiae has been classically viewed as an example of unicellular, eukaryotic different iation that occurs in response to nutritional starvation. We present e vidence that S. cerevisiae produces an extracellular factor(s), called meiosis-promoting factor (MEP), that is required, in addition to star vation conditions, for efficient meiosis and sporulation. This factor is secreted and accumulates in a cell density-dependent fashion such t hat cells at a low density sporulate poorly under conditions in which cells at a high density sporulate efficiently. Conditioned medium from sporulating cells at a high density contains a small anionic molecule that has cytostatic activity and stimulates sporulation of cells at l ow density under a normal starvation condition. These results indicate that MEP-mediated social communication between cells is required for meiosis and sporulation. (C) 1998 John Wiley & Sons, Ltd.