The organization of endoplasmic reticulum export complexes

A polyclonal antibody specific for yeast Sec23p that cross-reacts with a mammalian homologue (Orci et al., 1991) was obtained from R. Schekman (University of California, Berkeley). Affinity-purified antibodies specific for yeast Secl3p that cross-reacts with a mammalian homologue (Shaywitz et al., 1995) were a generous gift of C. Kaiser (Massachusetts Institute of Technology, Cambridge, MA). A hybridoma cell line expressing an mAb specific for the carboxyl terminus of vesicular stomafitis virus glycoprotein (VSV-G) (P5D4) was provided by T. Kreis (University of Geneva, Switzerland) (Kreis, 1986) . Secondary antibodies were obtained from the following sources: Texas red--conjugated goat anti-mouse IgG from Zymed Laboratories (South San Francisco, CA), 6 nm gold--conjugated goat anti-mouse and anti-rabbit antibodies from Jackson Immunoresearch Laboratories (West Groven, PA), and 10 nm gold--conjugated goat anti-mouse antibodies from Amersham Corp. (Arlington Heights, IL). Sarl wild type and the H79G and T39N mutant proteins were prepared as described (Aridor et al., 1995) . All other reagents, except where indicated, were obtained from Sigma Chemical Co. (St. Louis, MO).