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Vol. 17, Issue 11, 4780-4789, November 2006

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Erv26p Directs Pro-Alkaline Phosphatase into Endoplasmic Reticulum–derived Coat Protein Complex II Transport Vesicles

Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755

Submitted May 25, 2006; Revised August 15, 2006; Accepted August 21, 2006
Monitoring Editor: Akihiko Nakano

Secretory proteins are exported from the endoplasmic reticulum (ER) in transport vesicles formed by the coat protein complex II (COPII). We detected Erv26p as an integral membrane protein that was efficiently packaged into COPII vesicles and cycled between the ER and Golgi compartments. The erv26 mutant displayed a selective secretory defect in which the pro-form of vacuolar alkaline phosphatase (pro-ALP) accumulated in the ER, whereas other secretory proteins were transported at wild-type rates. In vitro budding experiments demonstrated that Erv26p was directly required for packaging of pro-ALP into COPII vesicles. Moreover, Erv26p was detected in a specific complex with pro-ALP when immunoprecipitated from detergent-solublized ER membranes. Based on these observations, we propose that Erv26p serves as a transmembrane adaptor to link specific secretory cargo to the COPII coat. Because ALP is a type II integral membrane protein in yeast, these findings imply that an additional class of secretory cargo relies on adaptor proteins for efficient export from the ER.

This article was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E06-05-0455) on September 6, 2006.

Address correspondence to: Charles Barlowe (barlowe{at}darmouth.edu)

Abbreviations used: ALP, alkaline phosphatase; CPY, carboxypeptidase Y; COPII, coat protein complex II; gpf, glycopro--factor; UPR, unfolded protein response; UPRE, UPR response element