title: Characterization of temperature-sensitive mutations in the yeast syntaxin 1 homologues Sso1p and Sso2p, and evidence of a distinct function for Sso1p in sporulation.
abstract: The duplicated genes SSO1 and SSO2 encode yeast homologues of syntaxin 1 and perform an essential function during fusion of secretory vesicles at the plasma membrane. We have used in vitro mutagenesis to obtain a temperature-sensitive SSO2 allele, sso2-1, in which a conserved arginine has been changed to a lysine. A yeast strain that lacks SSO1 and carries the sso2-1 allele ceases growth and accumulates secretory vesicles at the restrictive temperature. Interestingly, the strain also has a pronounced phenotype at the permissive temperature, causing a defect in bud neck closure that prevents separation of mother and daughter cells. The same mutation was introduced into SSO1, producing the sso1-1 allele, which also has a temperature-sensitive phenotype, although less pronounced than sso2-1. A screen for high copy number suppressors of sso2-1 yielded three genes that are involved in the terminal step of secretion: SNC1, SNC2 and SEC9. The sso1-1 mutation interacts synthetically with a disruption of the MSO1 gene, which encodes a Sec1p interacting protein. Interestingly, we further found that both MSO1 and SSO1, but not SSO2, are required for sporulation. This difference is not due to differential expression, since SSO2 expressed from the SSO1 promoter failed to restore sporulation. We conclude that a functional difference exists between the Sso1 and Sso2 proteins, with the former being specifically required during sporulation.
authors.affiliation: VTT Biotechnology, PO Box 1500, FIN-02044 VTT, Finland.
authors.forename: Jussi
authors.initials: J
authors.lastname: Jäntti
authors.forename: Markku K
authors.initials: MK
authors.lastname: Aalto
authors.forename: Mattias
authors.initials: M
authors.lastname: Oyen
authors.forename: Lena
authors.initials: L
authors.lastname: Sundqvist
authors.forename: Sirkka
authors.initials: S
authors.lastname: Keränen
authors.forename: Hans
authors.initials: H
authors.lastname: Ronne
mesh_terms: D000483:Alleles; D000954:Antigens, Surface / Q000235:genetics / Q000378:metabolism*; D012634:Bodily Secretions / Q000378:metabolism; D002455:Cell Division / Q000502:physiology; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D050765:Qa-SNARE Proteins; D050767:Qc-SNARE Proteins; D050683:R-SNARE Proteins; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins; D022142:Secretory Vesicles / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D013172:Spores, Fungal / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D050827:Syntaxin 1; D013696:Temperature
chemical_list: D000954:Antigens, Surface; D005656:Fungal Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; D050767:Qc-SNARE Proteins; D050683:R-SNARE Proteins; C090117:SEC9 protein, S cerevisiae; C083241:SNC1 protein, S cerevisiae; C083242:SNC2 protein, S cerevisiae; C084006:SSO1 protein, S cerevisiae; C084007:SSO2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D050827:Syntaxin 1