Ferro-Novick S, Novick P, Field C, Schekman R
J Cell Biol. 1984 Jan;98(1):35-43. doi: 10.1083/jcb.98.1.35.
Yeast cells secrete a variety of glycosylated proteins. At least two of these proteins, invertase and acid phosphatase, fail to be secreted in a new class of mutants that are temperature-sensitive for growth. Unlike the yeast secretory mutants previously described (class A sec mutants; Novick, P., C. Field, and R. Schekman, 1980, Cell., 21:205-420), class B sec mutants (sec 53, sec 59) fail to produce active secretory enzymes at the restrictive temperature (37 degrees C). sec 53 and sec 59 appear to be defective in reactions associated with the endoplasmic reticulum. Although protein synthesis continues at a nearly normal rate for 2 h at 37 degrees C, incorporation of [3H]mannose into glycoprotein is reduced. Immunoreactive polypeptide forms of invertase accumulate within the cell which have mobilities on SDS PAGE consistent with incomplete glycosylation: sec 53 produces little or no glycosylated invertase, and sec 59 accumulates forms containing 0-3 of the 9-10 N-linked oligosaccharide chains that are normally added to the protein. In addition to secreted enzymes, maturation of the vacuolar glycoprotein carboxypeptidase Y, incorporation of the plasma membrane sulfate permease activity, and secretion of the major cell wall proteins are blocked at 37 degrees C.
酵母细胞分泌多种糖基化蛋白。其中至少有两种蛋白，即转化酶和酸性磷酸酶，在一类对生长温度敏感的新突变体中无法分泌。与先前描述的酵母分泌突变体（A类sec突变体；诺维克，P.，C. 菲尔德，和R. 谢克曼，1980年，《细胞》，21:205 - 420）不同，B类sec突变体（sec 53、sec 59）在限制温度（37摄氏度）下无法产生有活性的分泌酶。sec 53和sec 59似乎在内质网相关反应中存在缺陷。尽管在37摄氏度下蛋白质合成能以接近正常的速率持续2小时，但[3H]甘露糖掺入糖蛋白的过程减少。转化酶的免疫反应性多肽形式在细胞内积累，其在SDS - PAGE上的迁移率与糖基化不完全一致：sec 53产生很少或不产生糖基化的转化酶，而sec 59积累的形式含有正常添加到该蛋白上的9 - 10条N - 连接寡糖链中的0 - 3条。除了分泌酶外，液泡糖蛋白羧肽酶Y的成熟、质膜硫酸盐通透酶活性的掺入以及主要细胞壁蛋白的分泌在37摄氏度时均受阻。
