Glycosylphosphatidylinositol-anchored proteins (GPI-APs) undergo extensive post-translational modifications and remodeling including the addition and subsequent removal of phospho-ethanolamine (EtNP) from mannose 1 (Man1) and mannose 2 (Man2) of the glycan moiety. Removal of EtNP from Man1 is catalyzed by Cdc1p, an event that has previously been considered to occur in the ER. We establish that Cdc1p is in fact a cis / medial Golgi membrane protein that relies on COPI coatomer for its retention in this organelle. We also determine that Cdc1p does not cycle between the Golgi and the ER, and consistent with this finding, when expressed at endogenous levels ER-localized Cdc1p-HDEL is unable to support the growth of cdc1Δ cells. Our cdc1 temperature-sensitive alleles are defective in the transport of a prototypical GPI-AP - Gas1p to the cell surface, a finding we posit reveals a novel Golgi-localized quality control warrant. Thus, yeast cells scrutinize GPI-APs in the ER and also in the Golgi, where removal of EtNP from Man2 (via Ted1p in the ER) and from Man1 (by Cdc1p in the Golgi) functions as a quality assurance signal.

糖基磷脂酰肌醇锚定蛋白 (GPI-AP) 经历广泛的翻译后修饰和重塑，包括添加和随后从聚糖部分的甘露糖 1 (Man1) 和甘露糖 2 (Man2) 中去除磷酸乙醇胺 (EtNP)。Cdc1p 催化 EtNP 从 Man1 中去除，这一事件以前被认为发生在 ER 中。我们确定 Cdc1p 实际上是一种顺式/内侧高尔基体膜蛋白，依赖于 COPI 外壳蛋白保留在该细胞器中。我们还确定 Cdc1p 不在高尔基体和 ER 之间循环，并且与这一发现一致，当以内源水平表达时，ER 定位的 Cdc1p-HDEL 无法支持cdc1Δ细胞的生长。我们的cdc1温度敏感等位基因在将原型 GPI-AP - Gas1p 运输到细胞表面方面存在缺陷，我们认为这一发现揭示了一种新颖的高尔基体本地化质量控制保证。因此，酵母细胞会仔细检查内质网和高尔基体中的 GPI-AP，其中从 Man2（通过内质网中的 Ted1p）和 Man1（通过高尔基体中的 Cdc1p）去除 EtNP 作为质量保证信号。