Biogenesis of the signal recognition particle (SRP) involves import of SRP proteins into the nucleolus, assembly with the SRP-RNA, and Xpo1p-mediated export.

摘要: The signal recognition particle (SRP) targets nascent secretory proteins to the ER, but how and where SRP assembles is largely unknown. Here we analyze biogenesis of yeast SRP, which consists an RNA molecule (scR1) six proteins, by localizing all its components. Although scR1 cytoplasmic in wild-type cells, nuclear localization was observed cells lacking any one four “core proteins” Srp14p, Srp21p, Srp68p, or Srp72p. Consistently, a major nucleolar pool detected for these proteins. Sec65p, on other hand, found both nucleoplasm nucleolus, whereas Srp54p predominantly cytoplasmic. Import core into nucleolus requires ribosomal protein import receptors Pse1p Kap123p/Yrb4p, might, thus, constitute pathway. Nuclear export mediated receptor Xpo1p, distinct from mRNA transport, requires, as evidenced accumulation dis3/rrp44 exosome component mutant, intact 3′ end. A subset nucleoporins, including Nsp1p Nup159p (Rat7p), are also necessary efficient translocation nucleus cytoplasm. We propose that assembly they assemble pre-SRP with scR1. This can then be targeted pores subsequently exported cytoplasm Xpo1p-dependent way.