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J. Cell Biol.,
Volume 143, Number 5, November 30, 1998 1167-1182
Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel
Members of the synaptobrevin/VAMP family of v-SNAREs are thought to be essential for vesicle
docking and exocytosis in both lower and higher eukaryotes. Here, we describe yeast mutants that appear
to bypass the known v-SNARE requirement in secretion. Recessive mutations in either VBM1 or VBM2,
which encode related ER-localized membrane proteins,
allow yeast to grow normally and secrete in the absence
of Snc v-SNAREs. These mutants show selective alterations in protein transport, resulting in the differential
trafficking and secretion of certain protein cargo. Yet,
processing of the vacuolar marker, carboxypeptidase Y,
and the secreted protein, invertase, appear normal in
these mutants indicating that general protein trafficking early in the pathway is unaffected. Interestingly, VBM1 and VBM2 are allelic to ELO3 and ELO2, two
genes that have been shown recently to mediate the
elongation of very long chain fatty acids and subsequent ceramide and inositol sphingolipid synthesis.
Thus, the v-SNARE requirement in constitutive exocytosis is abrogated by mutations in early components of
the secretory pathway that act at the level of lipid synthesis to affect the ability of secretory vesicles to sort
and deliver protein cargo.
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