Brodsky J L, Goeckeler J, Schekman R
Department of Biological Sciences, University of Pittsburgh, PA 15260, USA.
Proc Natl Acad Sci U S A. 1995 Oct 10;92(21):9643-6. doi: 10.1073/pnas.92.21.9643.
Two interacting heat shock cognate proteins in the lumen of the yeast endoplasmic reticulum (ER), Sec63p and BiP (Kar2p), are required for posttranslational translocation of yeast alpha-factor precursor in vitro. To investigate the role of these proteins in cotranslational translocation, we examined the import of invertase into wild-type, sec63, and kar2 mutant yeast membranes. We found that Sec63p and Kar2p are necessary for both co- and posttranslational translocation in yeast. Several kar2 mutants, one of which had normal ATPase activity, were defective in cotranslational translocation of invertase. We conclude that the requirement for BiP/Kar2p, which is not seen in a reaction reconstituted with pure mammalian membrane proteins [Görlich, D. & Rapoport, T.A. (1993) Cell 75, 615-630], is not due to a distinction between cotranslational translocation in mammalian cells and posttranslational translocation in yeast cells.
酵母内质网（ER）腔中的两种相互作用的热休克同源蛋白Sec63p和BiP（Kar2p）是体外酵母α因子前体翻译后转运所必需的。为了研究这些蛋白在共翻译转运中的作用，我们检测了蔗糖酶导入野生型、sec63和kar2突变型酵母膜的情况。我们发现Sec63p和Kar2p对于酵母中的共翻译和翻译后转运都是必需的。几个kar2突变体，其中一个具有正常的ATP酶活性，在蔗糖酶的共翻译转运中存在缺陷。我们得出结论，对于BiP/Kar2p的需求（这在由纯哺乳动物膜蛋白重构的反应中未观察到[Görlich, D. & Rapoport, T.A. (1993) Cell 75, 615 - 630]），并非由于哺乳动物细胞中的共翻译转运与酵母细胞中的翻译后转运之间的差异。
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