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J. Cell Biol.,
Volume 142, Number 2, July 27, 1998 443-455
Department of Pharmacology, Cornell University, Ithaca, New York 14853
The Rho-type GTPase Cdc42p has been implicated in diverse cellular functions including cell
shape, cell motility, and cytokinesis, all of which involve
the reorganization of the actin cytoskeleton. Targets of
Cdc42p that interface the actin cytoskeleton are likely candidates for mediating cellular activities. In this report, we identify and characterize a yeast homologue
for the mammalian IQGAP, a cytoskeletal target for
Cdc42p. The yeast IQGAP homologue, designated
Iqg1p, displays a two-hybrid interaction with activated Cdc42p and coimmunoprecipitates with actin filaments.
Deletion of IQG1 results in a temperature-sensitive lethality and causes aberrant morphologies including
elongated and round multinucleated cells. This together with its localization at the mother-bud neck, suggest that Iqg1p promotes budding and cytokinesis.
At restrictive temperatures, the vacuoles of the mutant
cells enlarge and vesicles accumulate in the bud. Interestingly, Iqg1p shows two-hybrid interactions with the
ankyrin repeat-containing protein, Akr1p (Kao, L.-R., J. Peterson, J. Ruiru, L. Bender, and A. Bender. 1996. Mol. Cell. Biol. 16:168-178), which inhibits pheromone
signaling and appears to promote cytokinesis and/or
trafficking. We also show two-hybrid interactions between Iqg1p and Afr1p, a septin-binding protein involved in projection formation (Konopka, J.B., C. DeMattei, and C. Davis. 1995. Mol. Cell. Biol. 15:723-730).
We propose that Iqg1p acts as a scaffold to recruit and
localize a protein complex involved in actin-based cellular functions and thus mediates the regulatory effects
of Cdc42p on the actin cytoskeleton.
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