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© The Rockefeller University Press, 0021-9525/1997//1511 $5.00
The Journal of Cell Biology, Volume 137, Number 7, , 1997 1511-1524

Article

The Yeast v-SNARE Vti1p Mediates Two Vesicle Transport Pathways through Interactions with the t-SNAREs Sed5p and Pep12p



Gabriele Fischer von Mollard, Steven F. Nothwehr, and Tom H. Stevens

Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403-1229

Membrane traffic in eukaryotic cells requires that specific v-SNAREs on transport vesicles interact with specific t-SNAREs on target membranes. We identified a novel Saccharomyces cerevisiae v-SNARE (Vti1p) encoded by the essential gene, VTI1. Vti1p interacts with the prevacuolar t-SNARE Pep12p to direct Golgi to prevacuolar traffic. vti1-1 mutant cells missorted and secreted the soluble vacuolar hydrolase carboxypeptidase Y (CPY) rapidly and reversibly when vti1-1 cells were shifted to the restrictive temperature. However, overexpression of Pep12p suppressed the CPY secretion defect exhibited by vti1-1 cells at 36°C. Characterization of a second vti1 mutant, vti1-11, revealed that Vti1p also plays a role in membrane traffic at a cis-Golgi stage. vti1-11 mutant cells displayed a growth defect and accumulated the ER and early Golgi forms of both CPY and the secreted protein invertase at the nonpermissive temperature. Overexpression of the yeast cis-Golgi t-SNARE Sed5p suppressed the accumulation of the ER form of CPY but did not lead to CPY transport to the vacuole in vti1-11 cells. Overexpression of Sed5p allowed growth in the absence of Vti1p. In vitro binding and coimmunoprecipitation studies revealed that Vti1p interacts directly with the two t-SNAREs, Sed5p and Pep12p. These data suggest that Vti1p plays a role in cis-Golgi membrane traffic, which is essential for yeast viability, and a nonessential role in the fusion of Golgi-derived vesicles with the prevacuolar compartment. Therefore, a single v-SNARE can interact functionally with two different t-SNAREs in directing membrane traffic in yeast.

1. Abbreviations used in this paper: CPY, carboxypeptidase Y; ER, endoplasmic reticulum; FOA, fluoroorotic acid.

Please address all correspondence to Tom H. Stevens, Institute of Molecular Biology, University of Oregon, Eugene, OR 97403-1229. Tel.: (541) 346-5884; Fax: (541) 346-4854; E-mail: stevens{at}molbio.uoregon.edu

S.F. Nothwehr's present address is Division of Biological Sciences, University of Missouri, Columbia, MO 65211


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