title: Subunits of the Saccharomyces cerevisiae signal recognition particle required for its functional expression.
abstract: The signal recognition particle (SRP) is an evolutionarily conserved ribonucleoprotein (RNP) complex that functions in protein targeting to the endoplasmic reticulum (ER) membrane. Only two protein subunits of the SRP, Srp54p and Sec65p, and the RNA subunit, scR1, were previously known in the yeast Saccharomyces cerevisiae. Purification of yeast SRP by immunoaffinity chromatography revealed five additional proteins. Amino acid sequencing and cloning of the genes encoding four of these proteins demonstrated that the yeast SRP contains homologs (termed Srp14p, Srp68p and Srp72p) of the SRP14, SRP68 and SRP72 subunits found in mammalian SRP. The yeast SRP also contains a 21 kDa protein (termed Srp21p) that is not homologous to any protein in mammalian SRP. An additional 7 kDa protein may correspond to the mammalian SRP9. Disruption of any one of the four genes encoding the newly identified SRP proteins results in slow cell growth and inefficient protein translocation across the ER membrane. These phenotypes are indistinguishable from those resulting from the disruption of genes encoding SRP components identified previously. These data indicate that a lack of any of the analyzed SRP components results in loss of SRP function. ScR1 RNA and SRP proteins are at reduced levels in cells lacking any one of the newly identified proteins. In contrast, SRP components are present at near wild type levels and SRP subparticles are present in cells lacking either Srp54p or Sec65p. Thus Srp14p, Srp21p, Srp68p and Srp72p, but not Sec65p or Srp54p, are required for stable expression of the yeast SRP.
authors.affiliation: Department of Biochemistry and Biophysics, University of California at San Francisco 94143-0448.
authors.forename: J D
authors.initials: JD
authors.lastname: Brown
authors.forename: B C
authors.initials: BC
authors.lastname: Hann
authors.forename: K F
authors.initials: KF
authors.lastname: Medzihradszky
authors.forename: M
authors.initials: M
authors.lastname: Niwa
authors.forename: A L
authors.initials: AL
authors.lastname: Burlingame
authors.forename: P
authors.initials: P
authors.lastname: Walter
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport; D003001:Cloning, Molecular; D017124:Conserved Sequence; D005656:Fungal Proteins / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification; D005800:Genes, Fungal / Q000235:genetics*; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D011233:Precipitin Tests; D011499:Protein Processing, Post-Translational; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid; D018271:Signal Recognition Particle / Q000235:genetics*
chemical_list: D005656:Fungal Proteins; D010455:Peptides; C489551:SEC65 protein, S cerevisiae; C089642:SRP14 protein, S cerevisiae; C089644:SRP21 protein, S cerevisiae; C082929:SRP68 protein, S cerevisiae; C503638:SRP72 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D018271:Signal Recognition Particle