Wiederkehr Andreas, Du Yunrui, Pypaert Marc, Ferro-Novick Susan, Novick Peter
Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Mol Biol Cell. 2003 Dec;14(12):4770-82. doi: 10.1091/mbc.e03-04-0229. Epub 2003 Sep 5.
Sec3p is a component of the exocyst complex that tethers secretory vesicles to the plasma membrane at exocytic sites in preparation for fusion. Unlike all other exocyst structural genes, SEC3 is not essential for growth. Cells lacking Sec3p grow and secrete surprisingly well at 25 degrees C; however, late markers of secretion, such as the vesicle marker Sec4p and the exocyst subunit Sec8p, localize more diffusely within the bud. Furthermore, sec3Delta cells are strikingly round relative to wild-type cells and are unable to form pointed mating projections in response to alpha factor. These phenotypes support the proposed role of Sec3p as a spatial landmark for secretion. We also find that cells lacking Sec3p exhibit a dramatic defect in the inheritance of cortical ER into the bud, whereas the inheritance of mitochondria and Golgi is unaffected. Overexpression of Sec3p results in a prominent patch of the endoplasmic reticulum (ER) marker Sec61p-GFP at the bud tip. Cortical ER inheritance in yeast has been suggested to involve the capture of ER tubules at the bud tip. Sec3p may act in this process as a spatial landmark for cortical ER inheritance.
Sec3p是外泌体复合物的一个组成部分，它将分泌囊泡在胞吐位点连接到质膜上，为融合做准备。与所有其他外泌体结构基因不同，SEC3对细胞生长不是必需的。缺乏Sec3p的细胞在25摄氏度时生长和分泌情况惊人地良好；然而，分泌的晚期标记物，如囊泡标记物Sec4p和外泌体亚基Sec8p，在芽内的定位更为分散。此外，相对于野生型细胞，sec3Δ细胞显著呈圆形，并且在响应α因子时无法形成尖锐的交配突起。这些表型支持了Sec3p作为分泌的空间标志物的 proposed role。我们还发现，缺乏Sec3p的细胞在将皮质内质网遗传到芽中的过程中表现出严重缺陷，而线粒体和高尔基体的遗传则不受影响。Sec3p的过表达导致内质网（ER）标记物Sec61p-GFP在芽尖处出现明显的斑块。酵母中的皮质内质网遗传被认为涉及在芽尖捕获内质网管。Sec3p可能在此过程中作为皮质内质网遗传的空间标志物发挥作用。
