Control of cell size and cycle time in Schizosaccharomyces pombe.

Steady-state and perturbed cells of Schizosaccharomyces pombe have been observed through several division cycles by time-lapse photomicrography. Perturbed cells were produced by the use of a conditional cell division cycle mutant in which nuclear division is reversibly blocked at high temperature. These experiments show that in both populations cell length at division and cell cycle duration are homeostatically controlled, probably by a primary size-control mechanism. Cycle time is indirectly controlled, as cells which have an extended cycle are on average larger at division, so that duaghters of such cells need to grow by a smaller amount and for a shorter period, before dividing again. In general, deviations from the mean are corrected within a single cycle, but in the case of very long cells the control breaks down because the cycle cannot be shortened by more than a quarter under the conditions used. These cells take more than one cycle to return to normal.