Orlean P, Schwaiger H, Appeltauer U, Haselbeck A, Tanner W
Eur J Biochem. 1984 Apr 2;140(1):183-9. doi: 10.1111/j.1432-1033.1984.tb08084.x.
alpha Factor specifically inhibits the synthesis of N-glycosylated proteins in Saccharomyces cerevisiae mating type a cells but not in alpha cells or in a/alpha diploids. a Factor has the same effect of alpha cells. The synthesis of O-glycosylated proteins is not inhibited. Although the mating pheromones act like a 'physiological tunicamycin', the mechanism of inhibition is different: not the glycosylation of proteins as such but rather the synthesis of those proteins destined to be N-glycosylated is inhibited. Thus none of a number of glycosylating enzymes tested in vitro is reduced in activity in alpha-factor-treated cells. The synthesis of the glycoprotein carboxypeptidase Y, on the other hand, is strongly inhibited by tunicamycin as well as by alpha factor; but only in the former case did carbohydrate-free protein accumulate in the cells. alpha Factor causes maximal inhibition of glycoprotein formation after as little as 30 min, long before all cells in the population are arrested in G1; moreover, release from this inhibition precedes the increase in budding index (resumption of cell division). It is postulated, therefore, that N-glycosylated proteins are required for the G1/S-phase transition in the yeast cell cycle. This is supported by previous reports that first cycle arrest in G1 occurs when (a) tunicamycin is added to growing cultures, and (b) a temperature-sensitive N-glycosylation mutant is shifted to its restrictive temperature.
α因子特异性抑制酿酒酵母a交配型细胞中N-糖基化蛋白的合成，但不抑制α细胞或a/α二倍体细胞中的合成。a因子对α细胞有相同的作用。O-糖基化蛋白的合成未受抑制。尽管交配信息素的作用类似于“生理性衣霉素”，但其抑制机制不同：不是抑制蛋白质本身的糖基化，而是抑制那些注定要进行N-糖基化的蛋白质的合成。因此，在体外测试的多种糖基化酶中，没有一种在经α因子处理的细胞中活性降低。另一方面，糖蛋白羧肽酶Y的合成受到衣霉素和α因子的强烈抑制；但只有在前一种情况下，无碳水化合物的蛋白质才会在细胞中积累。α因子在短短30分钟后就会对糖蛋白形成产生最大抑制，远在群体中的所有细胞都停滞在G1期之前；此外，从这种抑制中释放先于出芽指数的增加（细胞分裂的恢复）。因此，推测N-糖基化蛋白是酵母细胞周期中G1/S期转换所必需的。这得到了先前报告的支持，即当（a）将衣霉素添加到生长的培养物中，以及（b）将温度敏感的N-糖基化突变体转移到其限制温度时，首次在G1期发生细胞周期停滞。
