title: Kel1p Mediates Yeast Cell Fusion Through a Fus2p- and Cdc42p-Dependent Mechanism.
abstract: Cell fusion is ubiquitous among eukaryotes. Although little is known about the molecular mechanism, several proteins required for cell fusion in the yeast Saccharomyces cerevisiae have been identified. Fus2p, a key regulator of cell fusion, localizes to the shmoo tip in a highly regulated manner. C-terminal truncations of Fus2p cause mislocalization and fusion defects, which are suppressed by overexpression of Kel1p, a kelch-domain protein of unknown function previously implicated in cell fusion. We hypothesize that Fus2p mislocalization is caused by auto-inhibition, which is alleviated by Kel1p overexpression. Previous work showed that Fus2p localization is mediated by both Fus1p- and actin-dependent pathways. We show that the C-terminal mutations mainly affect the actin-dependent pathway. Suppression of the Fus2p localization defect by Kel1p is dependent upon Fus1p, showing that suppression does not bypass the normal pathway. Kel1p and a homolog, Kel2p, are required for efficient Fus2p localization, acting through the actin-dependent pathway. Although Kel1p overexpression can weakly suppress the mating defect of a FUS2 deletion, the magnitude of suppression is allele specific. Therefore, Kel1p augments, but does not bypass, Fus2p function. Fus2p mediates cell fusion by binding activated Cdc42p Although Kel1p overexpression suppresses a Cdc42p mutant that is defective for Fus2p binding, cell fusion remains dependent upon Fus2p These data suggest that Fus2p, Cdc42p, and Kel1p form a ternary complex, which is stabilized by Kel1p Supporting this hypothesis, Kel1p interacts with two domains of Fus2p, partially dependent on Cdc42p We conclude that Kel1p enhances the activity of Fus2p/Cdc42p in cell fusion.
authors: Department of Molecular Biology, Princeton University, New Jersey 08544.
authors: Jean A
authors: JA
authors: Smith
authors: Department of Molecular Biology, Princeton University, New Jersey 08544 mdrose@princeton.edu.
authors: Mark D
authors: http://orcid.org/0000-0003-1112-4765
authors: MD
authors: Rose
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D000595:Amino Acid Sequence; D002459:Cell Fusion; D003227:Conjugation, Genetic; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D018628:Gene Dosage; D008565:Membrane Proteins / Q000378:metabolism*; D009154:Mutation; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs / Q000235:genetics; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D015398:Signal Transduction; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D003598:Cytoskeletal Proteins; C095898:FUS2 protein, S cerevisiae; C489835:KEL1 protein, S cerevisiae; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D020764:cdc42 GTP-Binding Protein
keywords: conjugation; kelch protein; yeast mating