Holthuis J C, Nichols B J, Pelham H R
Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 2QH, United Kingdom.
Mol Biol Cell. 1998 Dec;9(12):3383-97. doi: 10.1091/mbc.9.12.3383.
Tlg1p and Tlg2p, members of the syntaxin family of SNAREs in yeast, have been implicated in both endocytosis and the retention of late Golgi markers. We have investigated the functions of these and the other endocytic syntaxins Pep12p and Vam3p. Remarkably, growth is possible in the absence of all four proteins. In the absence of the others, Pep12p and Tlg1p can each create endosomes accessible to the endocytic tracer dye FM4-64. However, although Pep12p is required for the ligand-induced internalization of the alpha factor receptor and its passage via Pep12p-containing membranes to the vacuole, Tlg1p is not. In contrast, Tlg1p is required for the efficient localization of the catalytic subunit of chitin synthase III (Chs3p) to the bud neck, a process that involves endocytosis and polarized delivery of Chs3p. In wild-type cells, internalized Chs3p cofractionates with Tlg1p and Tlg2p, and in a strain lacking the other endocytic syntaxins, either Tlg1p or Tlg2p is sufficient for correct localization of the enzyme. Pep12p is neither necessary nor sufficient for this process. We conclude that there are two endocytic routes in yeast that can operate independently and that Tlg1p is located at the junction of one of these with the polarized exocytic pathway.
Tlg1p和Tlg2p是酵母中SNARE蛋白 syntaxin家族的成员，它们与胞吞作用以及晚期高尔基体标志物的保留都有关联。我们研究了这些蛋白以及其他胞吞作用相关的syntaxin蛋白Pep12p和Vam3p的功能。值得注意的是，在这四种蛋白全部缺失的情况下细胞仍可生长。在其他蛋白缺失时，Pep12p和Tlg1p各自都能产生可被胞吞示踪染料FM4-64进入的内体。然而，尽管配体诱导的α因子受体内化及其通过含Pep12p的膜进入液泡需要Pep12p，但Tlg1p并非如此。相反，几丁质合酶III（Chs3p）催化亚基有效定位于芽颈需要Tlg1p，这一过程涉及Chs3p的胞吞作用和极性运输。在野生型细胞中，内化的Chs3p与Tlg1p和Tlg2p共分离，并且在缺乏其他胞吞作用相关syntaxin蛋白的菌株中，Tlg1p或Tlg2p中的任何一个对于该酶的正确定位都足够了。Pep12p对于这一过程既非必需也不充分。我们得出结论，酵母中有两条可以独立运作的胞吞途径，并且Tlg1p位于其中一条途径与极性分泌途径的交汇处。
