The mechanisms employed in the retention of Golgi resident membrane proteins are diverse and include features such as the composition and length of the protein's transmembrane domain and motifs that mediate direct or indirect associations with COPI-coatomer. However, in sum the current compendium of mechanisms cannot account for the localization of all Golgi membrane proteins, and this is particularly the case for proteins such as the glycosyltransferases. Here we describe a novel mechanism that mediates the steady-state retention of a subset of glycosyltransferases in the Golgi of budding yeast cells. This mechanism is mediated by a de-ubiquitinase complex comprised of Bre5p and Ubp3p. We show that in the absence of this de-ubiquitinase certain glycosyltransferases are mislocalized to the vacuole where they are degraded. We also show that Bre5p/Ubp3p clients bind to COPI-coatomer via a series of positively charged amino acids in their cytoplasmically exposed N-termini. Furthermore, we identify two proteins (Ktr3p and Mnn4p) that show a requirement for both Bre5p/Ubp3p as well as the COPI-coatomer affiliated sorting receptor Vps74p. We also establish that some proteins show a nutrient-dependent role for Vps74p in their Golgi retention. This study expands the repertoire of mechanisms mediating the retention of Golgi membrane proteins.

用于保留高尔基体驻留膜蛋白的机制是多种多样的，并且包括诸如蛋白跨膜结构域的组成和长度以及介导与COPI-涂层剂直接或间接缔合的基序等特征。然而，总的来说，当前的机制简述不能解释所有高尔基体膜蛋白的定位，并且对于诸如糖基转移酶的蛋白尤其如此。在这里，我们描述了一种介导糖基转移酶子集在发芽酵母细胞的高尔基体中的稳态保留的新机制。该机制由包含Bre5p和Ubp3p的去泛素酶复合物介导。我们表明，在缺少这种去泛素化酶的情况下，某些糖基转移酶被错误地定位到液泡处，在液泡处它们被降解。我们还显示，Bre5p / Ubp3p客户通过其细胞质暴露的N末端中的一系列带正电荷的氨基酸与COPI-coatomer结合。此外，我们确定了两种蛋白质（Ktr3p和Mnn4p），它们显示了Bre5p / Ubp3p以及COPI-coatomer关联分选受体Vps74p的需求。我们还建立了一些蛋白质在其高尔基体保留中显示Vps74p营养依赖的作用。这项研究扩大了介导高尔基体膜蛋白保留机制的库。我们还建立了一些蛋白质在其高尔基体保留中显示Vps74p营养依赖的作用。这项研究扩大了介导高尔基体膜蛋白保留机制的库。我们还建立了一些蛋白质在其高尔基体保留中显示Vps74p营养依赖的作用。这项研究扩大了介导高尔基体膜蛋白保留机制的库。