CHANGES IN PAF (PLATELET-ACTIVATING-FACTOR) PRODUCTION DURING CELL-CYCLE OF YEAST SACCHAROMYCES-CEREVISIAE

Yeast Saccharomyces cerevisiae cells were cultured synchronously and t he change of platelet-activating factor (PAF) production during the ce ll cycle was investigated at each phase of the cycle. The basal PAF co ntents of diploid AKU4103 cells in G1 and M phases were higher than th ose of cells in S phase. Both diploid and haploid strains showed the s ame level of PAF production in response to the calcium ionophore A2318 7. A23187-stimulated PAF productions of cells in G1 and M phases were about 20 times higher than that of cells in S phase. The contents of P AF precursor in G1 and M phases cells of AKU4103 were higher than thos e in S phase cells, and the ratio of A23187-stimulated PAF to the prec ursor was highest in G1 phase cells. We also examined the change in a PAF-synthesizing enzyme, acetyltransferase, activity during the cell c ycle using a microsomal fraction. Specific activity was the highest at G1 phase, and total activity was higher at M phase. The enzyme activi ties of cells in S phase of strains AKU4103 and RAY-3Aa were one-third and one-tenth of those in G1 phase of corresponding cells, respective ly. These results suggest that PAF production was higher at G1 and M p hases and lower at S phase, and changes in PAF productivity during cel l cycle were related to the precursor contents and the synthesizing en zyme activities in those cells. These data suggest that PAF may contro l the cell cycle phase in budding yeast.