De Craene Johan-Owen, Coleman Jeff, Estrada de Martin Paula, Pypaert Marc, Anderson Scott, Yates John R, Ferro-Novick Susan, Novick Peter
Department of Cell Biology and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA.
Mol Biol Cell. 2006 Jul;17(7):3009-20. doi: 10.1091/mbc.e06-01-0080. Epub 2006 Apr 19.
The endoplasmic reticulum (ER) contains both cisternal and reticular elements in one contiguous structure. We identified rtn1Delta in a systematic screen for yeast mutants with altered ER morphology. The ER in rtn1Delta cells is predominantly cisternal rather than reticular, yet the net surface area of ER is not significantly changed. Rtn1-green fluorescent protein (GFP) associates with the reticular ER at the cell cortex and with the tubules that connect the cortical ER to the nuclear envelope, but not with the nuclear envelope itself. Rtn1p overexpression also results in an altered ER structure. Rtn proteins are found on the ER in a wide range of eukaryotes and are defined by two membrane-spanning domains flanking a conserved hydrophilic loop. Our results suggest that Rtn proteins may direct the formation of reticulated ER. We independently identified Rtn1p in a proteomic screen for proteins associated with the exocyst vesicle tethering complex. The conserved hydophilic loop of Rtn1p binds to the exocyst subunit Sec6p. Overexpression of this loop results in a modest accumulation of secretory vesicles, suggesting impaired exocyst function. The interaction of Rtn1p with the exocyst at the bud tip may trigger the formation of a cortical ER network in yeast buds.
内质网（ER）在一个连续的结构中包含池状和网状成分。我们在对具有内质网形态改变的酵母突变体进行的系统筛选中鉴定出了rtn1Delta。rtn1Delta细胞中的内质网主要是池状而非网状，然而内质网的净表面积没有显著变化。Rtn1-绿色荧光蛋白（GFP）与细胞皮层的网状内质网以及将皮层内质网与核膜相连的小管相关联，但不与核膜本身相关联。Rtn1p的过表达也会导致内质网结构改变。Rtn蛋白在广泛的真核生物的内质网上被发现，并由位于保守亲水性环两侧的两个跨膜结构域所定义。我们的结果表明，Rtn蛋白可能指导网状内质网的形成。我们在一项针对与外泌体囊泡拴系复合体相关蛋白质的蛋白质组学筛选中独立鉴定出了Rtn1p。Rtn1p保守的亲水性环与外泌体亚基Sec6p结合。该环的过表达导致分泌囊泡适度积累，表明外泌体功能受损。Rtn1p与芽尖处的外泌体之间的相互作用可能触发酵母芽中皮层内质网网络的形成。
