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The Journal of Cell Biology, Vol 131, 57-67, Copyright © 1995 by The Rockefeller University Press
ARTICLES |
C Itin, R Schindler and HP Hauri
Department of Pharmacology, University of Basel, Switzerland.
ERGIC-53 is a lectin-type membrane protein that continuously recycles between the ER, ER-Golgi intermediate compartment (ERGIC) and the cis- Golgi. To identify the targeting signals that mediate this recycling, N- glycosylated and myc-tagged variants of ERGIC-53 were constructed. By monitoring endoglycosidase H resistance, we measured the loss from the ER-ERGIC-cis-Golgi cycle of ERGIC-53. A domain exchange approach with the plasma membrane reporter protein CD4 showed that the transmembrane and the lumenal domains are not sufficient, while the cytoplasmic domain of ERGIC-53 is required and sufficient for pre-medial-Golgi localization. However, the ERGIC-53 cytoplasmic domain on CD4 lead to increased ER-staining by immunofluorescence microscopy indicating that this domain alone cannot provide for unbiased recycling through the ER- ERGIC-cis-Golgi compartments. Complete progress through the ER-ERGIC- cis-Golgi recycling pathway requires the cytoplasmic domain acting together with the lumenal domain of ERGIC-53. Dissection of the cytoplasmic domain revealed a COOH-terminal di-lysine ER-retrieval signal, KKFF, and an RSQQE targeting determinant adjacent to the transmembrane domain. Surprisingly, the two COOH-terminal phenylalanines influence the targeting. They reduce the ER-retrieval capacity of the di-lysine signal and modulate the RSQQE determinant.
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