Function of cortical domains of the endoplasmic reticulum

真核细胞利用分泌(SEC)途径进行质膜蛋白的生物发生。我们最近对模式生物酿酒酵母的研究表明，存在另一种将完整的膜蛋白运输到质膜的途径。Ist2p蛋白从内质网(ER)转运到细胞表面，不依赖于经典SEC途径的功能。我们已经确定Ist2p(Ist2c)的胞浆C-末端结构域是质膜的主要靶向信号。当这个结构域位于其他膜蛋白的C末端时，它会将产生的嵌合体重定向到质膜上。由于这一机制主要是通过将蛋白质靶向其他膜来进行的，我们假设Ist2p的生物发生是通过在ER的特定结构域上的局部合成来启动的。最有可能的是，这些结构域位于细胞的外围，蛋白质从那里通过未知的机制到达质膜。为了找到Ist2p运输所需的因素，我们将纯化Ist2c相互作用蛋白并进行遗传筛选，以确定这一新途径所需的基因。

Eukaryotic cells use the secretory (SEC)-pathway for the biogenesis of plasma membrane proteins. Our recent studies with the model organism Saccharomyces cerevisiae have shown that an alternative pathway exists for the trafficking of an integral membrane protein to the plasma membrane. The protein Ist2p is transported from the endoplasmic reticulum (ER) to the cell surface independently of the function of the classical SEC-pathway. We have identified the cytosolic C-terminal domain of Ist2p (Ist2c) as a dominant targeting signal for the plasma membrane. When this domain is positioned at the C-terminus of other membrane proteins, it redirects the resulting chimeras to the plasma membrane. Since this mechanism operates dominantly over the targeting of proteins to other membranes, we postulate that the biogenesis of Ist2p is initiated by a local synthesis at specific domains of the ER. Most likely these domains are positioned at the cell periphery from where the protein travels by an unknown mechanism to the plasma membrane. In order to find the factors that are required for the trafficking of Ist2p, we will purify Ist2c-interacting proteins and perform a genetic screen to identify the required genes for this novel pathway.