The secretory pathway mediates localization of the cell polarity regulator Aip3p/Bud6p.
Aip3p/Bud6p is a regulator of cell and cytoskeletal polarity in Saccharomyces cerevisiae that was previously identified as an actin-interacting protein. Actin-interacting protein 3 (Aip3p) localizes at the cell cortex where cytoskeleton assembly must be achieved to execute polarized cell growth, and deletion of AIP3 causes gross defects in cell and cytoskeletal polarity. We have discovered that Aip3p localization is mediated by the secretory pathway. Mutations in early- or late-acting components of the secretory apparatus lead to Aip3p mislocalization. Biochemical data show that a pool of Aip3p is associated with post-Golgi secretory vesicles. An investigation of the sequences within Aip3p necessary for Aip3p localization has identified a sequence within the N terminus of Aip3p that is sufficient for directing Aip3p localization. Replacement of the N terminus of Aip3p with a homologous region from a Schizosaccharomyces pombe protein allows for normal Aip3p localization, indicating that the secretory pathway-mediated Aip3p localization pathway is conserved. Delivery of Aip3p also requires the type V myosin motor Myo2p and its regulatory light-chain calmodulin. These data suggest that one function of calmodulin is to activate Myo2p's activity in the secretory pathway; this function is likely the polarized movement of late secretory vesicles and associated Aip3p on actin cables.
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State University of New York Upstate Medical University, Department of Biochemistry and Molecular Biology, Syracuse, New York 13210, USA.
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D000595:Amino Acid Sequence; D001692:Biological Transport; D002147:Calmodulin / Q000235:genetics / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology; D016764:Cell Polarity; D017124:Conserved Sequence / Q000235:genetics; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D005800:Genes, Fungal / Q000235:genetics / Q000502:physiology; D006056:Golgi Apparatus / Q000502:physiology; D008840:Microfilament Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008861:Microsomes / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D018995:Myosin Heavy Chains; D024462:Myosin Type II; D024701:Myosin Type V; D009218:Myosins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D021382:Protein Sorting Signals / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D012568:Schizosaccharomyces / Q000235:genetics; D029702:Schizosaccharomyces pombe Proteins; D016415:Sequence Alignment; D013696:Temperature; D013997:Time Factors; D014617:Vacuoles / Q000378:metabolism; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology
C107727:BUD6 protein, S cerevisiae; C499541:Bud6 protein, S pombe; D002147:Calmodulin; D002352:Carrier Proteins; D005656:Fungal Proteins; C077512:MYO2 protein, S cerevisiae; C434211:MYO2 protein, S pombe; D008840:Microfilament Proteins; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D024462:Myosin Type II; D024701:Myosin Type V; D018995:Myosin Heavy Chains; D009218:Myosins; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae