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Binding to membrane proteins within the endoplasmic reticulum cannot explain the retention of the glucose‐regulated protein GRP78 in Xenopus oocytes.
Author(s) -
Ceriotti A.,
Colman A.
Publication year - 1988
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1988.tb02857.x
Subject(s) - endoplasmic reticulum , xenopus , biology , kdel , oocyte , glucose regulated protein , er retention , microbiology and biotechnology , secretory protein , secretion , biochemistry , unfolded protein response , golgi apparatus , gene , embryo , mutant
We have studied the compartmentation and movement of the rat 78‐kd glucose‐regulated protein (GRP78) and other secretory and membrane proteins in Xenopus oocytes. Full length GRP78, normally found in the lumen of rat endoplasmic reticulum (ER), is localized to a membraneous compartment in oocytes and is not secreted. A truncated GRP78 lacking the C‐terminal (KDEL) ER retention signal is secreted, although at a slow rate. When the synthesis of radioactive GRP78 is confined to a polar (animal or vegetal) region of the oocyte and the subsequent movement across the oocyte monitored, we find that both full‐length and truncated GRP78 move at similar rates and only slightly slower than a secretory protein, chick ovalbumin. In contrast, a plasma membrane protein (influenza haemagglutinin) and two ER membrane proteins (rotavirus VP10 and a mutant haemagglutinin) remained confined to their site of synthesis. We conclude that the retention of GRP78 in the ER is not due to its tight binding to a membrane‐bound receptor.