Biogenesis of the signal recognition particle (SRP) involves import of SRP proteins into the nucleolus, assembly with the SRP-RNA, and Xpo1p-mediated export.
The signal recognition particle (SRP) targets nascent secretory proteins to the ER, but how and where the SRP assembles is largely unknown. Here we analyze the biogenesis of yeast SRP, which consists of an RNA molecule (scR1) and six proteins, by localizing all its components. Although scR1 is cytoplasmic in wild-type cells, nuclear localization was observed in cells lacking any one of the four SRP "core proteins" Srp14p, Srp21p, Srp68p, or Srp72p. Consistently, a major nucleolar pool was detected for these proteins. Sec65p, on the other hand, was found in both the nucleoplasm and the nucleolus, whereas Srp54p was predominantly cytoplasmic. Import of the core proteins into the nucleolus requires the ribosomal protein import receptors Pse1p and Kap123p/Yrb4p, which might, thus, constitute a nucleolar import pathway. Nuclear export of scR1 is mediated by the nuclear export signal receptor Xpo1p, is distinct from mRNA transport, and requires, as evidenced by the nucleolar accumulation of scR1 in a dis3/rrp44 exosome component mutant, an intact scR1 3' end. A subset of nucleoporins, including Nsp1p and Nup159p (Rat7p), are also necessary for efficient translocation of scR1 from the nucleus to the cytoplasm. We propose that assembly of the SRP requires import of all SRP core proteins into the nucleolus, where they assemble into a pre-SRP with scR1. This particle can then be targeted to the nuclear pores and is subsequently exported to the cytoplasm in an Xpo1p-dependent way.
Grosshans
H
H
Biochemie-Zentrum Heidelberg, D-69120 Heidelberg, Germany.
Deinert
K
K
Hurt
E
E
Simos
G
G
D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins / Q000378:metabolism*; D002466:Cell Nucleolus / Q000378:metabolism*; D003001:Cloning, Molecular; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D049452:Green Fluorescent Proteins; D017404:In Situ Hybridization, Fluorescence; D007202:Indicators and Reagents / Q000378:metabolism; D028884:Karyopherins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation / Q000502:physiology; D022022:Nuclear Pore / Q000378:metabolism; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D012331:RNA, Fungal / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear; D012269:Ribosomal Proteins / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D018271:Signal Recognition Particle / Q000235:genetics* / Q000378:metabolism*; D015003:Yeasts; D000097606:Exportin 1 Protein
D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D005656:Fungal Proteins; D049452:Green Fluorescent Proteins; D007202:Indicators and Reagents; D028884:Karyopherins; D008164:Luminescent Proteins; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins; D012331:RNA, Fungal; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; D018271:Signal Recognition Particle; D000097606:Exportin 1 Protein; C062748:NSP1 protein, S cerevisiae; C089642:SRP14 protein, S cerevisiae; C089644:SRP21 protein, S cerevisiae; C082929:SRP68 protein, S cerevisiae; C503638:SRP72 protein, S cerevisiae