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Vol. 14, Issue 1, 26-39, January 2003


Department of Biochemistry and Molecular Biology, Louisiana State
University Health Sciences Center, Shreveport, Louisiana 71130
Bni4 is a scaffold protein in the yeast Saccharomyces
cerevisiae that tethers chitin synthase III to the bud neck by
interacting with septin neck filaments and with Chs4, a regulatory
subunit of chitin synthase III. We show herein that Bni4 is also a
limiting determinant for the targeting of the type 1 serine/threonine
phosphatase (Glc7) to the bud neck. Yeast cells containing a Bni4
variant that fails to associate with Glc7 fail to tether Chs4 to the
neck, due in part to the failure of Bni4V831A/F833A to
localize properly. Conversely, the Glc7-129 mutant protein fails
to bind Bni4 properly and glc7-129 mutants exhibit
reduced levels of Bni4 at the bud neck. Bni4 is phosphorylated in a
cell cycle-dependent manner and Bni4V831A/F833A is both
hyperphosphorylated and mislocalized in vivo. Yeast cells lacking the
protein kinase Hsl1 exhibit increased levels of Bni4-GFP at the bud
neck. GFP-Chs4 does not accumulate at the incipient bud site in either
a bni4::TRP1 or a
bni4V831A/F833A mutant but does
mobilize to the neck at cytokinesis. Together, these results indicate
that the formation of the Bni4-Glc7 complex is required for
localization to the site of bud emergence and for subsequent targeting
of chitin synthase.
Online version of this article contains video material for
some figures. Online version available at
www.molbiolcell.org.
*
These authors contributed equally to this work.
Present addresses:
Department of Biochemistry, 140 Farber
Hall, SUNY, Buffalo, NY 14214;
Division of Basic Science
Fred Hutchinson Cancer Research Center, 1100 Fairfiew Ave, North,
Seattle, WA 98105; and
§GlaxoSmithKline, 709 Swedeland
Rd., P.O. Box 1539, King of Prussia, PA 19406.
Corresponding author. E-mail address:
ktatch{at}lsuhsc.edu.
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