title: Iqg1p links spatial and secretion landmarks to polarity and cytokinesis.
abstract: Cytokinesis requires the polarization of the actin cytoskeleton, the secretion machinery, and the correct positioning of the division axis. Budding yeast cells commit to their cytokinesis plane by choosing a bud site and polarizing their growth. Iqg1p (Cyk1p) was previously implicated in cytokinesis (Epp and Chant, 1997; Lippincott and Li, 1998; Osman and Cerione, 1998), as well as in the establishment of polarity and protein trafficking (Osman and Cerione, 1998). To better understand how Iqg1p influences these processes, we performed a two-hybrid screen and identified the spatial landmark Bud4p as a binding partner. Iqg1p can be coimmunoprecipitated with Bud4p, and Bud4p requires Iqg1p for its proper localization. Iqg1p also appears to specify axial bud-site selection and mediates the proper localization of the septin, Cdc12p, as well as binds and helps localize the secretion landmark, Sec3p. The double mutants iqg1Deltasec3Delta and bud4Deltasec3Delta display defects in polarity, budding pattern and cytokinesis, and electron microscopic studies reveal that these cells have aberrant septal deposition. Taken together, these findings suggest that Iqg1p recruits landmark proteins to form a targeting patch that coordinates axial budding with cytokinesis.
authors.affiliation: Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA. mo28@cornell.edu
authors.forename: Mahasin A
authors.initials: MA
authors.lastname: Osman
authors.forename: James B
authors.initials: JB
authors.lastname: Konopka
authors.forename: Richard A
authors.initials: RA
authors.lastname: Cerione
mesh_terms: D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002455:Cell Division / Q000502:physiology*; D016764:Cell Polarity; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D046911:Macromolecular Substances; D008954:Models, Biological; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000502:physiology / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D020703:ras GTPase-Activating Proteins
chemical_list: C100763:BUD4 protein, S cerevisiae; C099504:CDC12 protein, S cerevisiae; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; D005656:Fungal Proteins; C101203:IQ motif containing GTPase activating protein 1; D046911:Macromolecular Substances; D011993:Recombinant Fusion Proteins; C103130:SEC3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D020703:ras GTPase-Activating Proteins; D019204:GTP-Binding Proteins