Moore S A
Department of Chemistry and Biochemistry, University of Guelph, Ontario, Canada.
J Biol Chem. 1988 Jul 15;263(20):9674-81.
The kinetics of cell cycle initiation were measured at pH 2.7 for cells that had been arrested at the "start" step of cell division with the polypeptide pheromone alpha-factor. Cell cycle initiation was induced by the removal of alpha-factor. The rate at which cells completed start was identical to the rate of subsequent bud emergence. After short times of prearrest with alpha-factor (e.g. 5.2 h), the kinetics of bud emergence were biphasic, indicative of two subpopulations of cells that differed by greater than 10-fold in their rates of cell cycle initiation. The subpopulation that exhibited a slow rate of cell cycle initiation is comprised of cells that resided in G1 prior to start at the time of removal of alpha-factor, whereas the subpopulation that initiated the cell cycle rapidly is comprised of cells that had reached and become blocked at start. A critical concentration of cycloheximide was found to reintroduce slow budding cells into a population of 100% fast budding cells, suggesting that the two subpopulations differ with respect to attainment of a critical rate of protein synthesis that is necessary for the performance of start. Cycloheximide and an increase in the time of prearrest with alpha-factor had opposite effects on both the partitioning of cells between the two subpopulations and the net rate of protein synthesis per cell, consistent with this conclusion. Cell cycle initiation by the subpopulation of fast budding cells required protein synthesis even though the critical rate of protein synthesis had been achieved during arrest. It is concluded that alpha-factor inhibits the synthesis of and/or inactivates specific proteins that are required for the performance of start, but alpha-factor does not prevent attainment of the critical rate of protein synthesis.
在pH 2.7条件下，测定了被多肽信息素α-因子阻滞在细胞分裂“起始”步骤的细胞的细胞周期起始动力学。通过去除α-因子诱导细胞周期起始。细胞完成起始的速率与随后出芽的速率相同。用α-因子预阻滞短时间（如5.2小时）后，出芽动力学呈双相性，表明存在两个亚群的细胞，它们的细胞周期起始速率相差超过10倍。细胞周期起始速率较慢的亚群由在去除α-因子时处于起始之前G1期的细胞组成，而快速起始细胞周期的亚群由已经到达起始并被阻滞在起始的细胞组成。发现临界浓度的环己酰亚胺可将慢出芽细胞重新引入100%快出芽细胞群体中，这表明这两个亚群在达到起始所需的临界蛋白质合成速率方面存在差异。环己酰亚胺和延长用α-因子预阻滞的时间对两个亚群之间细胞的分配以及每个细胞的蛋白质合成净速率都有相反的影响，这与该结论一致。尽管在阻滞期间已经达到了临界蛋白质合成速率，但快出芽细胞亚群的细胞周期起始仍需要蛋白质合成。得出的结论是，α-因子抑制起始所需的特定蛋白质的合成和/或使其失活，但α-因子并不阻止达到临界蛋白质合成速率。
