Effects of temperature and nutritional conditions on the mitotic cell cycle of Saccharomyces cerevisiae.

Yeast cells were cultivated at different growth rates in a chemostat by alterations in the flow of the limiting nutrient glucose and in batch cultures where variations in growth rate were achieved by alterations in the composition of nutrients. It was observed that the stage in the cycle at which S-phase was completed varied with growth rate. The faster the growth rate, the earlier the stage in the cycle in which completion of S-phase occurred. When stage in the cycle is converted into time before division it was observed that the time from completion of S-phase to cell division varied only slightly with growth rate except at extremely slow growth rates. Expansion of cell cycle transit time as the growth rate was slowed was achieved primarily by an expansion in time of the period from division to the completion of S-phase. In contrast, when cells were grown at different rates by alterations in the temperature of cultivation, completion of S-phase occurred at approximately the same stage in the cell cycle at all growth rates.