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J. Cell Biol.,
Volume 143, Number 4, November 16, 1998 935-946
Department of Molecular Biology, Vanderbilt University, Nashville, Tennessee 37235
The yeast
-1,3-mannosyltransferase
(Mnn1p) is localized to the Golgi by independent transmembrane and lumenal domain signals. The lumenal
domain is localized to the Golgi complex when expressed as a soluble form (Mnn1-s) by exchange of its
transmembrane domain for a cleavable signal sequence
(Graham, T. R., and V. A. Krasnov. 1995. Mol. Biol.
Cell. 6:809-824). Mutants that failed to retain the lumenal domain in the Golgi complex, called lumenal domain retention (ldr) mutants, were isolated by screening mutagenized yeast colonies for those that secreted
Mnn1-s. Two genes were identified by this screen,
HOG1, a gene encoding a mitogen-activated protein kinase (MAPK) that functions in the high osmolarity
glycerol (HOG) pathway, and LDR1. We have found
that basal signaling through the HOG pathway is required to localize Mnn1-s to the Golgi in standard osmotic conditions. Mutations in HOG1 and LDR1 also
perturb localization of intact Mnn1p, resulting in its loss
from early Golgi compartments and a concomitant increase of Mnn1p in later Golgi compartments.
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