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J. Cell Biol.,
Volume 142, Number 5, September 7, 1998 1209-1222
Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755
COPII-coated ER-derived transport vesicles
from Saccharomyces cerevisiae contain a distinct set of
membrane-bound polypeptides. One of these polypeptides, termed Erv14p (ER-vesicle protein of 14 kD),
corresponds to an open reading frame on yeast chromosome VII that is predicted to encode an integral
membrane protein and shares sequence identity with
the Drosophila cornichon gene product. Experiments
with an epitope-tagged version of Erv14p indicate that
this protein localizes to the ER and is selectively packaged into COPII-coated vesicles. Haploid cells that lack
Erv14p are viable but display a modest defect in bud
site selection because a transmembrane secretory protein, Axl2p, is not efficiently delivered to the cell surface. Axl2p is required for selection of axial growth
sites and normally localizes to nascent bud tips or the mother bud neck. In erv14
strains, Axl2p accumulates
in the ER while other secretory proteins are transported at wild-type rates. We propose that Erv14p is required for the export of specific secretory cargo from
the ER. The polarity defect of erv14 yeast cells is reminiscent of cornichon mutants, in which egg chambers fail to establish proper asymmetry during early stages
of oogenesis. These results suggest an unforeseen conservation in mechanisms producing cell polarity shared
between yeast and Drosophila.
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