Mammalian Vesicle Trafficking Proteins of the Endoplasmic Reticulum and Golgi Apparatus

doi:10.1074/jbc.271.10.5671

Mammalian Vesicle Trafficking Proteins of the Endoplasmic Reticulum and Golgi Apparatus (*)

From the Howard Hughes Medical Institute, Department of Molecular and Cellular Physiology, Stanford University Medical Center, Stanford, California 94305-5428

^¶ To whom correspondence should be addressed. Tel.: 415-723-9075; Fax: 415-725-4436.

Abstract

Vesicle traffic propagates and maintains distinct subcellular compartments and routes secretory products from their site of synthesis to their final destinations. As a basis for the specificity of vesicular transport reactions, each step in the secretory pathway appears to be handled by a distinct set of evolutionarily conserved proteins. Mammalian proteins responsible for vesicle trafficking at early steps in the secretory pathway are not well understood. In this report, we describe rat sec22 (rsec22) and rat bet1 (rbet1), mammalian sequence homologs of yeast proteins identified as mediators of endoplasmic reticulum-to-Golgi protein transport. rsec22 and rbet1 were expressed widely in mammalian tissues, as anticipated for proteins involved in fundamental membrane trafficking reactions. Recombinant rsec22 and rbet1 proteins behaved as integral membrane components of 28 and 18 kDa, respectively, consistent with their primary structures, which contain a predicted transmembrane domain at or near the carboxyl terminus. Recombinant rsec22 and rbet1 had distinct subcellular localizations, with rsec22 residing on endoplasmic reticulum membranes and rbet1 found on Golgi membranes. Studies with brefeldin A and nocodazole indicated that rbet1 function might involve interaction with or retention in the intermediate compartment. The distinct localizations of rsec22 and rbet1 may reflect their participation in opposite directions of membrane flow between the endoplasmic reticulum and Golgi apparatus.

Footnotes

↵^§ Recipient of a European Molecular Biology Organization long-term fellowship.
↵* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank(™)/EMBL Data Bank with accession number(s) U42209 and U42755.
↵¹ The abbreviations used are:

ER

endoplasmic reticulum

VAMP

vesicle-associated membrane protein

rsec22

rat sec22

rbet1

rat bet1

EST

expressed sequence tag

bp

base pair(s)

kb

kilobase pair(s)

PCR

polymerase chain reaction

BFA

brefeldin A

PBS

phosphate-buffered saline

β-COP

β-coatomer protein.
- Received September 25, 1995.
- Revision received December 12, 1995.