title: Carboxy terminal modifications of the P0 protein reveal alternative mechanisms of nuclear ribosomal stalk assembly.
abstract: The P0 scaffold protein of the ribosomal stalk is mainly incorporated into pre-ribosomes in the cytoplasm where it replaces the assembly factor Mrt4. In analyzing the role of the P0 carboxyl terminal domain (CTD) during ribosomal stalk assembly, we found that its complete removal yields a protein that is functionally similar to Mrt4, whereas a chimeric Mrt4 containing the P0 CTD behaves more like P0. Deleting the P0 binding sites for the P1 and P2 proteins provoked the nuclear accumulation of P0ΔAB induced by either leptomycin B-mediated blockage of nuclear export or Mrt4 deletion. This effect was reversed by removing P1/P2 from the cell, whereas nuclear accumulation was restored on reintroduction of these proteins. Together, these results indicate that the CTD determines the function of the P0 in stalk assembly. Moreover, they indicate that in cells lacking Mrt4, P0 and its stalk base partner, the L12 protein, bind to pre-ribosomes in the nucleus, a complex that is then exported to the cytoplasm by a mechanism assisted by the interaction with P1/P2 proteins. Furthermore, in wild-type cells, the presence of nuclear pre-ribosome complexes containing P0 but not L12 is compatible with the existence of an alternative stalk assembly process.
authors.affiliation: Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid, 28049 Madrid.
authors.forename: Rosario
authors.initials: R
authors.lastname: Francisco-Velilla
authors.forename: Miguel
authors.initials: M
authors.lastname: Remacha
authors.forename: Juan P G
authors.initials: JP
authors.lastname: Ballesta
mesh_terms: D002467:Cell Nucleus / Q000378:metabolism*; D005456:Fluorescent Dyes; D017353:Gene Deletion; D049452:Green Fluorescent Proteins / Q000032:analysis / Q000235:genetics; D010750:Phosphoproteins / Q000235:genetics; D017434:Protein Structure, Tertiary; D012269:Ribosomal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D054683:Ribosome Subunits, Large, Eukaryotic / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics
chemical_list: D005456:Fluorescent Dyes; C121972:MRT4 protein, S cerevisiae; D010750:Phosphoproteins; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; C031937:phosphoprotein P2, ribosomal; C035690:ribosomal phosphoprotein P1; C054675:ribosomal protein P0; D049452:Green Fluorescent Proteins