A NITROGEN STARVATION-INDUCED DORMANT G(0) STATE IN FISSION YEAST - THE ESTABLISHMENT FROM UNCOMMITTED G(1) STATE AND ITS DELAY FOR RETURN TO PROLIFERATION

Fission yeast cells either remain in the mitotic cell cycle or exit to meiotic sporulation from an uncommitted G(1) state dependent on the p resence or absence of nitrogen source in the medium (Nurse and Bissett , 1981). We examined how heterothallic haploid cells, which cannot spo rulate, behave under nitrogen-starvation for longer than 25 days at 26 degrees C. These cells were shown to enter a stable state (designated the dormant G(0)) with nearly full viability. Maintaining the dormant cells required glucose, suggesting that the cells remained metabolica lly active although cell division had ceased. They differed dramatical ly from mitotic and uncommitted G(1) cells in heat resistance, and als o in cytoplasmic and nuclear morphologies. After nitrogen replenishmen t, the initial responses of dormant G(0) cells were investigated. The kinetics for reentry into the proliferative state were delayed conside rably, and the changes in cell shape were enhanced particularly for th ose recovering from extended nitrogen starvation. A part of the delay could be accounted for by the duration of nuclear decondensation and c ell elongation for the first cell division.