Powers J, Barlowe C
Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
J Cell Biol. 1998 Sep 7;142(5):1209-22. doi: 10.1083/jcb.142.5.1209.
COPII-coated ER-derived transport vesicles from Saccharomyces cerevisiae contain a distinct set of membrane-bound polypeptides. One of these polypeptides, termed Erv14p (ER-vesicle protein of 14 kD), corresponds to an open reading frame on yeast chromosome VII that is predicted to encode an integral membrane protein and shares sequence identity with the Drosophila cornichon gene product. Experiments with an epitope-tagged version of Erv14p indicate that this protein localizes to the ER and is selectively packaged into COPII-coated vesicles. Haploid cells that lack Erv14p are viable but display a modest defect in bud site selection because a transmembrane secretory protein, Axl2p, is not efficiently delivered to the cell surface. Axl2p is required for selection of axial growth sites and normally localizes to nascent bud tips or the mother bud neck. In erv14Delta strains, Axl2p accumulates in the ER while other secretory proteins are transported at wild-type rates. We propose that Erv14p is required for the export of specific secretory cargo from the ER. The polarity defect of erv14Delta yeast cells is reminiscent of cornichon mutants, in which egg chambers fail to establish proper asymmetry during early stages of oogenesis. These results suggest an unforeseen conservation in mechanisms producing cell polarity shared between yeast and Drosophila.
来自酿酒酵母的COPII包被的内质网衍生转运囊泡含有一组独特的膜结合多肽。其中一种多肽，称为Erv14p（14 kD的内质网囊泡蛋白），对应于酵母第七条染色体上的一个开放阅读框，预计编码一种整合膜蛋白，并与果蝇的cornichon基因产物具有序列同一性。对带有表位标签的Erv14p版本进行的实验表明，该蛋白定位于内质网，并被选择性地包装到COPII包被的囊泡中。缺乏Erv14p的单倍体细胞是有活力的，但在芽位点选择上表现出适度的缺陷，因为一种跨膜分泌蛋白Axl2p不能有效地递送到细胞表面。Axl2p是选择轴向生长位点所必需的，通常定位于新生的芽尖或母芽颈部。在erv14Delta菌株中，Axl2p在内质网中积累，而其他分泌蛋白以野生型速率运输。我们提出，Erv14p是内质网中特定分泌货物输出所必需的。erv14Delta酵母细胞的极性缺陷让人联想到cornichon突变体，在该突变体中，卵室在卵子发生早期未能建立适当的不对称性。这些结果表明，酵母和果蝇在产生细胞极性的机制上存在意想不到的保守性。
