Roberg K J, Crotwell M, Espenshade P, Gimeno R, Kaiser C A
Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
J Cell Biol. 1999 May 17;145(4):659-72. doi: 10.1083/jcb.145.4.659.
In Saccharomyces cerevisiae, vesicles that carry proteins from the ER to the Golgi compartment are encapsulated by COPII coat proteins. We identified mutations in ten genes, designated LST (lethal with sec-thirteen), that were lethal in combination with the COPII mutation sec13-1. LST1 showed synthetic-lethal interactions with the complete set of COPII genes, indicating that LST1 encodes a new COPII function. LST1 codes for a protein similar in sequence to the COPII subunit Sec24p. Like Sec24p, Lst1p is a peripheral ER membrane protein that binds to the COPII subunit Sec23p. Chromosomal deletion of LST1 is not lethal, but inhibits transport of the plasma membrane proton-ATPase (Pma1p) to the cell surface, causing poor growth on media of low pH. Localization by both immunofluorescence microscopy and cell fractionation shows that the export of Pma1p from the ER is impaired in lst1Delta mutants. Transport of other proteins from the ER was not affected by lst1Delta, nor was Pma1p transport found to be particularly sensitive to other COPII defects. Together, these findings suggest that a specialized form of the COPII coat subunit, with Lst1p in place of Sec24p, is used for the efficient packaging of Pma1p into vesicles derived from the ER.
在酿酒酵母中，从内质网（ER）向高尔基体转运蛋白质的囊泡由II型被膜泡（COPII）包被蛋白包裹。我们鉴定出了10个基因的突变，这些基因被命名为LST（与sec13-1致死），它们与COPII突变体sec13-1组合时是致死的。LST1与整套COPII基因表现出合成致死相互作用，这表明LST1编码一种新的COPII功能。LST1编码的蛋白质在序列上与COPII亚基Sec24p相似。与Sec24p一样，Lst1p是一种内质网外周膜蛋白，可与COPII亚基Sec23p结合。LST1的染色体缺失并不致死，但会抑制质膜质子ATP酶（Pma1p）向细胞表面的转运，导致在低pH培养基上生长不良。免疫荧光显微镜和细胞分级分离定位均显示，在lst1Delta突变体中，Pma1p从内质网的输出受损。内质网中其他蛋白质的转运不受lst1Delta影响，Pma1p的转运也未发现对其他COPII缺陷特别敏感。总之，这些发现表明，一种特殊形式的COPII被膜亚基，用Lst1p取代Sec24p，用于将Pma1p高效包装到源自内质网的囊泡中。
