Cell cycle inhibition of yeast spheroplasts.

Osmotically stabilized yeast spheroplasts are capable of extensive DNA synthesis. Although the rate of DNA synthesis in spheroplasts is approximately one-third that of intact cells, the relative amounts of nuclear and mitochondrial DNA synthesized by spheroplasts is very similar to the relative amounts synthesized by intact cells. Furthermore, nuclear but not mitochondrial DNA synthesis is inhibited in MATa spheroplasts by the application of the yeast mating pheromone, alpha-factor. Similarly, DNA synthesis is reversibly temperature-sensitive in spheroplasts created from cdc7 and cdc8 mutant cells.