title: Stepwise and cooperative assembly of a cytokinetic core complex in Saccharomyces cerevisiae.
abstract: Actomyosin ring (AMR) contraction and the synthesis of an extracellular septum are interdependent pathways that mediate cytokinesis in the yeast Saccharomyces cerevisiae and other eukaryotes. How these interdependent pathways are physically connected is central for understanding cytokinesis. The yeast IQGAP (Iqg1p) belongs to the conserved AMR. The F-BAR-domain-containing protein Hof1p is a member of a complex that stimulates cell wall synthesis. We report here on the stepwise formation of a physical connection between both proteins. The C-terminal IQ-repeats of Iqg1p first bind to the essential myosin light chain before both proteins assemble with Hof1p into the Mlc1p-Iqg1p-Hof1p (MIH) bridge. Mutations in Iqg1p that disrupt the MIH complex alter Hof1p targeting to the AMR and impair AMR contraction. Epistasis analyses of two IQG1 alleles that are incompatible with formation of the MIH complex support the existence and functional significance of a large cytokinetic core complex. We propose that the MIH complex acts as hinge between the AMR and the proteins involved in cell wall synthesis and membrane attachment.
authors.affiliation: Institute of Molecular Genetics and Cell Biology, Department of Biology, Ulm University, James-Franck-Ring N27, 89081 Ulm, Germany.
authors.forename: Chen
authors.initials: C
authors.lastname: Tian
authors.affiliation: Institute of Molecular Genetics and Cell Biology, Department of Biology, Ulm University, James-Franck-Ring N27, 89081 Ulm, Germany.
authors.forename: Yehui
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Institute of Molecular Genetics and Cell Biology, Department of Biology, Ulm University, James-Franck-Ring N27, 89081 Ulm, Germany nils.johnsson@uni-ulm.de.
authors.forename: Nils
authors.initials: N
authors.lastname: Johnsson
mesh_terms: D048749:Cytokinesis; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D018994:Myosin Light Chains / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D020703:ras GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C116847:HOF1 protein, S cerevisiae; C101203:IQ motif containing GTPase activating protein 1; C113979:MLC1 protein, S cerevisiae; D008869:Microtubule-Associated Proteins; D018994:Myosin Light Chains; D029701:Saccharomyces cerevisiae Proteins; D020703:ras GTPase-Activating Proteins
keywords: Cytokinesis; F-BAR protein; IQGAP; Protein–protein interaction