Hamilton T G, Flynn G C
Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403, USA.
J Biol Chem. 1996 Nov 29;271(48):30610-3. doi: 10.1074/jbc.271.48.30610.
Proteins enter the secretory pathway by translocation across the endoplasmic reticulum (ER) membrane. In Saccharomyces cerevisiae, import of proteins into the ER occurs both cotranslationally and posttranslationally. Presumably, the cotranslational targeting to the ER membrane is directed by the signal recognition particle, as demonstrated in other eukaryotic systems. The deletion of a gene, called CER1, inhibits the translocation of proteins that enter the ER posttranslationally, but not those that enter cotranslationally. This translocation defect is more pronounced at lower temperatures. A strain possessing a null mutation of CER1 in combination with a kar2 temperature-sensitive mutation displays synthetic growth defects, whereas overexpression of the ER DnaJ homolog Scj1p suppresses the translocation defect in cer1Delta strains. CER1 is predicted to encode a 100-kDa polypeptide, residing in the ER lumen that is related to the hsp70 family of molecular chaperones.
蛋白质通过跨内质网（ER）膜转运进入分泌途径。在酿酒酵母中，蛋白质进入内质网的过程既发生在共翻译阶段，也发生在翻译后阶段。据推测，共翻译时靶向内质网膜是由信号识别颗粒引导的，这在其他真核系统中已得到证实。一种名为CER1的基因缺失会抑制翻译后进入内质网的蛋白质的转运，但不会影响共翻译进入内质网的蛋白质的转运。这种转运缺陷在较低温度下更为明显。一个具有CER1无效突变与kar2温度敏感突变的菌株表现出合成生长缺陷，而内质网DnaJ同源物Scj1p的过表达则抑制了cer1Delta菌株中的转运缺陷。预测CER1编码一种100 kDa的多肽，定位于内质网腔，与分子伴侣的hsp70家族相关。
