Growth and the cell cycle of the yeast Saccharomyces cerevisiae. I. Slowing S phase or nuclear division decreases the G1 cell cycle period.

Cells of the yeast Saccharomyces cerevisiae were subjected to a number of treatments which protracted S phase without proportional effects on growth processes. These treatments allowed steady-state exponential growth but lengthened the overall generation time. Such cells exhibited larger cell sizes and earlier performance of the cell cycle regulatory event 'start' and the two prereplicative steps defined by cdc4 and cdc7 mutations. Similarly, inhibiting progress through nuclear division with sub-arresting concentrations of methyl-benzimidazole-2-yl-carbamate also caused longer steady-state cell cycle times and earlier performance of 'start'. These findings underscore and extend earlier conclusions that most of the G1 interval of the yeast cell cycle is simply a period of ongoing growth. Conditions which protract any one of the periodic events in the division process without affecting growth will lead to the virtual elimination of the G1 interval.