Orci L, Palmer D J, Ravazzola M, Perrelet A, Amherdt M, Rothman J E
Institute of Histology and Embryology, University of Geneva Medical School, Switzerland.
Nature. 1993 Apr 15;362(6421):648-52. doi: 10.1038/362648a0.
Do the coats on vesicles budded from the Golgi apparatus actually cause the budding, or do they simply coat buds (Fig. 1)? One view (the membrane-mediated budding hypothesis) is that budding is an intrinsic property of Golgi membranes not requiring extrinsic coat proteins. Assembly of coats from dispersed subunits is super-imposed upon the intrinsic budding process and is proposed to convert the tips of tubules into vesicles. The alternative view (the coat-mediated budding hypothesis) is that coat formation provides the essential driving force for budding. The membrane-mediated budding hypothesis was inspired by the microtubule-dependent extension of apparently uncoated, 90-nm-diameter membrane tubules from the Golgi apparatus and other organelles in vivo after treatment with brefeldin A, a drug that inhibits the assembly of coat proteins onto Golgi membranes. This hypothesis predicts that tubules will be extended when coat proteins are unavailable to convert tubule-derived membrane into vesicles. Here we use a cell-free system in which coated vesicles are formed from Golgi cisternae to show that, on the contrary, when budding diminishes as a result of immunodepletion of coat protein pools, tubules are not formed at the expense of vesicles. We conclude that coat proteins are required for budding from Golgi membranes.
从高尔基体出芽形成的囊泡上的衣被，实际上是导致了出芽，还是仅仅覆盖芽体（图1）？一种观点（膜介导出芽假说）认为，出芽是高尔基体膜的固有特性，不需要外在的衣被蛋白。衣被从分散的亚基组装，是叠加在固有出芽过程之上的，并且被认为是将小管的末端转化为囊泡。另一种观点（衣被介导出芽假说）则认为，衣被的形成提供了出芽的基本驱动力。膜介导出芽假说是受到以下现象的启发：在用布雷菲德菌素A（一种抑制衣被蛋白组装到高尔基体膜上的药物）处理后，体内高尔基体和其他细胞器会出现明显无衣被的、直径90纳米的膜小管的微管依赖性延伸。该假说预测，当衣被蛋白无法将源自小管的膜转化为囊泡时，小管将会延伸。在这里，我们使用了一个无细胞系统，其中从高尔基体潴泡形成有衣被囊泡，结果表明，恰恰相反，当由于衣被蛋白池的免疫耗竭而出芽减少时，小管不会以囊泡为代价而形成。我们得出结论，从高尔基体膜出芽需要衣被蛋白。
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