KAR5 encodes a novel pheromone-inducible protein required for homotypic nuclear fusion.
KAR5 is required for membrane fusion during karyogamy, the process of nuclear fusion during yeast mating. To investigate the molecular mechanism of nuclear fusion, we cloned and characterized the KAR5 gene and its product. KAR5 is a nonessential gene, and deletion mutations produce a bilateral defect in the homotypic fusion of yeast nuclei. KAR5 encodes a novel protein that shares similarity with a protein in Schizosaccharomyces pombe that may play a similar role in nuclear fusion. Kar5p is induced as part of the pheromone response pathway, suggesting that this protein uniquely plays a specific role during mating in nuclear membrane fusion. Kar5p is a membrane protein with its soluble domain entirely contained within the lumen of the endoplasmic reticulum. In pheromone-treated cells, Kar5p was localized to the vicinity of the spindle pole body, the initial site of fusion between haploid nuclei during karyogamy. We propose that Kar5p is required for the completion of nuclear membrane fusion and may play a role in the organization of the membrane fusion complex.
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Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544-1014, USA.
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D000595:Amino Acid Sequence; D001483:Base Sequence; D001692:Biological Transport; D002451:Cell Compartmentation; D016764:Cell Polarity; D003001:Cloning, Molecular; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D000072235:Mating Factor; D008561:Membrane Fusion; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009685:Nuclear Envelope / Q000502:physiology*; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology; D010675:Pheromones / Q000494:pharmacology; D017433:Protein Structure, Secondary; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D017422:Sequence Analysis, DNA; D008941:Spindle Apparatus / Q000737:chemistry
D005656:Fungal Proteins; C109412:KAR5 protein, S cerevisiae; D008565:Membrane Proteins; D009687:Nuclear Proteins; D010455:Peptides; D010675:Pheromones; D029701:Saccharomyces cerevisiae Proteins; D000072235:Mating Factor