The appropriate delivery of secretory proteins to the correct subcellular destination is an essential cellular process. In the endoplasmic reticulum (ER), secretory proteins are captured into COPII vesicles that generally exclude ER resident proteins and misfolded proteins. We previously characterized a collection of yeast mutants that fail to enforce this sorting stringency and improperly secrete the ER chaperone, Kar2 (Copic et al., Genetics 2009). Here, we used the emp24Δ mutant strain that secretes Kar2 to identify candidate proteins that might regulate ER export, reasoning that loss of regulatory proteins would restore sorting stringency. We find that loss of the deubiquitylation complex Ubp3/Bre5 reverses all of the known phenotypes of the emp24Δ mutant, and similarly reverses Kar2 secretion of many other ER retention mutants. Based on a combination of genetic interactions and live cell imaging, we conclude that Ubp3 and Bre5 modulate COPII coat assembly at ER exit sites. Therefore, we propose that Ubp3/Bre5 influences the rate of vesicle formation from the ER that in turn can impact ER quality control events.

中文翻译：

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Ubp3/Bre5去泛素化复合物调节COPII囊泡形成

将分泌蛋白适当地递送到正确的亚细胞目的地是一个必不可少的细胞过程。在内质网 (ER) 中，分泌蛋白被捕获到通常排除 ER 驻留蛋白和错误折叠蛋白的 COPII 囊泡中。我们之前描述了一组酵母突变体，这些突变体未能强制执行这种分类严格性并且不正确地分泌 ER 伴侣 Kar2（Copic 等人，遗传学2009）。在这里，我们使用分泌 Kar2 的emp24Δ突变菌株来识别可能调节 ER 输出的候选蛋白，推断调节蛋白的丢失将恢复分选严格性。我们发现去泛素化复合物 Ubp3/Bre5 的缺失逆转了 emp24Δ 的所有已知表型突变体，并且类似地逆转了许多其他ER保留突变体的Kar2分泌。基于遗传相互作用和活细胞成像的结合，我们得出结论 Ubp3 和 Bre5 调节 ER 出口部位的 COPII 涂层组装。因此，我们建议 Ubp3/Bre5 影响 ER 囊泡形成的速率，进而影响 ER 质量控制事件。