MOLECULAR STUDIES OF EUKARYOTIC CELL SURFACE GROWTH

我们已经分离出一系列酵母分泌突变体（sec突变体）， 对细胞表面生长、分裂和分泌温度敏感。 大部分 这些突变体在细胞内库中积累分泌蛋白， 当细胞恢复到允许温度时释放。 至少23 基因产物已经牵涉到传递膜的过程， 分泌蛋白质到细胞表面。 电子显微镜分析 揭示了三种不同的膜结合细胞器，它们在不同的细胞中积累， 变种人 十个突变体产生囊泡，九个突变体产生 内质网，和两个突变体产生高尔基体样结构 我们称之为伯克利体 我们还发现了9个控制细胞最早期发育的基因 表面生长途径 这些基因的突变导致了 合成活性分泌蛋白质，尽管总体 蛋白质合成 其中两个突变体在产生一种 膜透性酶活性 分泌型突变体现在被用来鉴定一些 参与细胞表面生长的事件 在高等真核细胞中， 糖蛋白在转运至细胞的过程中分阶段糖基化 因此如果分泌突变体阻断了从一个阶段到另一个阶段的通道， 不完全糖基化的形式可能积累。 我们发现至少有两个 分泌酶转化酶上的寡糖组装阶段。 的 分泌突变体，积累内质网在一个非允许的 温度产生不完全糖基化形式转化酶。

We have isolated a series of yeast secretory mutants (sec mutants) that are temperature-sensitive for cell surface growth, division, and secretion. Most of these mutants accumulate secretory proteins in an intracellular pool which can be released when cells are returned to a permissive temperature. At least 23 gene products have been implicated in the process of delivering membrane and secretory proteins to the cell surface. Electron microscope analysis has revealed three distinct membrane-bounded organelles that accumulate in different mutants. Ten of the mutants produce vesicles, nine of the mutants produce endoplasmic reticulum, and two of the mutants produce Golgi body-like structures which we have called Berkely bodies. We have also identified nine genes that contrrl the earliest steps in the cell surface growth pathway. Mutations in these genes result in a failure to synthesize active secretory protein, in spite of a normal rate of overall protein synthesis. Two of the mutants are also defective in the production of a membrane permease activity. The secretory mutants are now being used to identify some of the molecular events involved in cell-surface growth. In higher eukaryotic cells, glycoproteins are glycosylated in stages during their transit to the cell surface and thus if a secretory mutant blocks passage from one stage to another, incompletely glycosylated forms may accumulate. We have detected at least two stages in oligosaccharide assembly on the secretory enzyme invertase. The secretory mutants that accumulate endoplasmic reticulum at a nonpermissive temperature produce an incompletely glycosylated form of invertase.