Moore S A
J Biol Chem. 1983 Nov 25;258(22):13849-56.
MAT alpha cells of the yeast Saccharomyces cerevisiae produce a polypeptide mating pheromone, alpha factor. MATa cells respond to the pheromone by undergoing several inducible responses: the arrest of cell division, the production of a cell surface agglutinin, and the formation of one or more projections on the cell surface commonly termed the "shmoo" morphology. Dose-response curves were determined for each of these inducible responses as a function of alpha factor concentration. It is shown that under conditions commonly employed in previous studies, the dose-response for cell division arrest is determined by the rate at which cells inactivate the alpha factor. In order to achieve conditions where inactivation would not be the dominant parameter, the cell division response to alpha factor was monitored at low cell densities. Under conditions of essentially no alpha factor destruction, the dose of alpha factor at which cells exhibit a half-maximal response for cell division arrest (2.5 X 10(-10) M) is nearly the same as that at which cells exhibit a half-maximal response for agglutination induction (1.0 X 10(-10) M). On the contrary, the half-maximal response for projection formation was obtained at doses of alpha factor 2 orders of magnitude higher (1.4 X 10(-8) M). These results are consistent with the same high affinity alpha factor receptor mediating both cell division arrest and agglutination induction. A different system of lower affinity must mediate projection formation. Alternatively, if the same system and receptor are used, then a much higher occupancy is required for the induction of projections compared to division arrest and agglutination induction.
酿酒酵母的 MATα 细胞会产生一种多肽交配信息素，即 α 因子。MATa 细胞对该信息素会产生几种诱导反应：细胞分裂停止、细胞表面凝集素的产生以及细胞表面形成一个或多个突起，通常称为“shmoo”形态。针对这些诱导反应中的每一种，都测定了其作为 α 因子浓度函数的剂量反应曲线。结果表明，在先前研究中常用的条件下，细胞分裂停止的剂量反应由细胞使 α 因子失活的速率决定。为了达到失活不是主导参数的条件，在低细胞密度下监测细胞对 α 因子的分裂反应。在基本没有 α 因子破坏的条件下，细胞对细胞分裂停止表现出半最大反应时的 α 因子剂量（2.5×10⁻¹⁰ M）与细胞对凝集诱导表现出半最大反应时的剂量（1.0×10⁻¹⁰ M）几乎相同。相反，形成突起的半最大反应是在 α 因子剂量高 2 个数量级（1.4×10⁻⁸ M）时获得的。这些结果与介导细胞分裂停止和凝集诱导的是相同的高亲和力 α 因子受体一致。较低亲和力的不同系统必定介导突起的形成。或者，如果使用相同的系统和受体，那么与分裂停止和凝集诱导相比，诱导突起需要更高的占据率。
