COPII Subunit Interactions in the Assembly of the Vesicle Coat*
- From the Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
Abstract
In vitro analysis of COPII vesicle formation in the yeast Saccharomyces cerevisiae has demonstrated the requirement for three cytosolic factors: Sec31p-Sec13p, Sec23p-Sec24p, and Sar1p. Convergent evidence suggests that the peripheral endoplasmic reticulum (ER) membrane protein Sec16p also represents an important component of the vesicle assembly apparatus: SEC16 interacts genetically with all five COPII genes; Sec16p binds to Sec23p and Sec24p, is found on ER-derived transport vesicles, and is required in vitro for the efficient release of ER-derived vesicle cargo. In this report, we demonstrate an important functional interaction between Sec16p and Sec31p. First, we map onto Sec31p binding regions for Sec16p, Sec23p, Sec24p, and Sec13p. Second, we show that a truncation mutant of Sec31p specifically defective for Sec16p binding is unable to complement asec31Δ mutant and cannot rescue the secretion defect of a temperature-sensitive sec31 mutant at nonpermissive temperatures. We propose that Sec16p organizes the assembly of a coat that is stabilized both by the interaction of Sec31p with Sec23p and Sec24p and by the interaction of these three components with Sec16p.
Footnotes
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↵* This work was supported by the National Science Foundation Division of Education and Centers, the NIGMS, National Institutes of Health, and the Searle Scholars Program (to C. A. K.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed. Tel.: 617-253-9804; Fax: 617-253-8699; E-mail: ckaiser{at}mit.edu.
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↵1 The abbreviations used are: ER, endoplasmic reticulum; GST, glutathione S-transferase; HA, hemagglutinin; PAGE, polyacrylamide gel electrophoresis; CPY, carboxypeptidase Y; 5-FOA, 5-fluoroorotic acid.
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↵2 R. Gimeno, unpublished observations.
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- Received July 21, 1997.
- Revision received August 17, 1997.
