Iqg1p, a yeast homologue of the mammalian IQGAPs, mediates cdc42p effects on the actin cytoskeleton.
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.
Osman
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Department of Pharmacology, Cornell University, Ithaca, New York 14853, USA.
Cerione
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D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002147:Calmodulin / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002455:Cell Division / Q000235:genetics; D002467:Cell Nucleus / Q000378:metabolism / Q000648:ultrastructure; D016764:Cell Polarity / Q000235:genetics; D002686:Chitin / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D017353:Gene Deletion; D008969:Molecular Sequence Data; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013696:Temperature; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae
D000199:Actins; D002147:Calmodulin; D018797:Cell Cycle Proteins; D017931:DNA Primers; D005656:Fungal Proteins; D020690:GTPase-Activating Proteins; D011506:Proteins; D002686:Chitin; D019204:GTP-Binding Proteins; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae