GENES REQUIRED FOR COMPLETION OF IMPORT OF PROTEINS INTO THE ENDOPLASMIC-RETICULUM IN YEAST
GENES REQUIRED FOR COMPLETION OF IMPORT OF PROTEINS INTO THE ENDOPLASMIC-RETICULUM IN YEAST
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DOI：
10.1083/jcb.98.1.44
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发表时间：
1984-01-01
影响因子：
7.8
通讯作者：
SCHEKMAN, R
中科院分区：
文献类型：
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作者：
FERRONOVICK, S;HANSEN, W;SCHEKMAN, R
酵母分泌突变体sec 53和sec 59定义了糖蛋白前体进入内质网（ER）的翻译后阶段。在限制温度（37 ℃）下，C）这些突变体积累分泌酶转化酶和液泡酶羧肽酶Y的酶失活和不完全糖基化形式。细胞分级分离实验表明，这些前体形式仍然主要牢固地结合到ER膜。当返回到允许温度（24 ℃）时，C），转化酶前体被糖基化，变得部分有活性并被分泌。热可逆转化不需要蛋白质合成，但需要能量。与这些突变的效果相反，在37 ℃下用衣霉素抑制寡糖合成。C引起非糖基化转化酶的不可逆积累。药物的作用被高温放大，因为在衣霉素存在下在25 ℃合成未糖基化的转化酶。C是隐藏的。一部分转化酶多肽在37 ℃下积累。当用胰蛋白酶处理sec 53和sec 59的膜时，C被保存下来。在Triton X-100或皂苷存在下，转化酶被完全降解。受保护的片段似乎代表嵌入ER膜或与ER膜牢固结合的转化酶多肽的一部分。这种关联可能在转化酶合成的早期发展，因此在没有易位的情况下，一些完整的多肽链仍然暴露在ER的细胞质表面上。
Yeast secretory mutants sec53 and sec59 define a posttranslational stage in the penetration of glycoprotein precursors into the endoplasmic reticulum (ER). At the restrictive temperature (37.degree. C) these mutants accumulate enzymatically inactive and incompletely glycosylated forms of the secretory enzyme invertase and the vacuolar enzyme carboxypeptidase Y. Cell fractionation experiments reveal that these precursor forms remain mainly firmly bound to the ER membrane. Upon return to the permissive temperature (24.degree. C), the invertase precursors are glycosylated, become partially active and are secreted. Thermoreversible conversion does not require protein synthesis, but does require energy. In contrast to the effect of these mutations, inhibition of oligosaccharide synthesis with tunicamycin at 37.degree. C causes irreversible accumulation of unglycosylated invertase. The effect of the drug is exaggerated by high temperature since unglycosylated invertase synthesized in the presence of tunicamycin at 25.degree. C is secreted. A portion of the invertase polypeptide accumulated at 37.degree. C is preserved when membranes from sec53 and sec59 are treated with trypsin. In the presence of Triton X-100 or saponin, the invertase is degraded completely. The protected fragment appears to represent a portion of the invertase polypeptide that is embedded in or firmly associated with the ER membrane. This association may develop early during the synthesis of invertase, so that in the absence of translocation, some of the completed polypeptide chain remains exposed on the cytoplasmic surface of the ER.