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Abstract
Yeast Saccharomyces cerevisiae cells were cultured synchronously and the change of platelet-activating factor (PAF) production during the cell cycle was investigated at each phase of the cycle. The basal PAF contents of diploid AKU4103 cells in G1 and M phases were higher than those of cells in S phase. Both diploid and haploid strains showed the same level of PAF production in response to the calcium ionophore Α23187. 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 PAF precursor in G1 and M phases cells of AKU4103 were higher than those in S phase cells, and the ratio of A23187-stimulated PAF to the precursor was highest in G1 phase cells. We also examined the change in a PAF-synthesizing enzyme, acetyltransferase, activity during the cell cycle using a microsomal fraction. Specific activity was the highest at G1 phase, and total activity was higher at M phase. The enzyme activities 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, respectively. These results suggest that PAF production was higher at G1 and M phases and lower at S phase, and changes in PAF productivity during cell cycle were related to the precursor contents and the synthesizing enzyme activities in those cells. These data suggest that PAF may control the cell cycle phase in budding yeast.