title: Ribosomal protein L12 uses a distinct nuclear import pathway mediated by importin 11.
abstract: Ribosome biogenesis requires the nuclear translocation of ribosomal proteins from their site of synthesis in the cytoplasm to the nucleus. Analyses of the import mechanisms have revealed that most ribosomal proteins can be delivered to the nucleus by multiple transport receptors (karyopherins or importins). We now provide evidence that ribosomal protein L12 (rpL12) is distinguished from the bulk of ribosomal proteins because it accesses the importin 11 pathway as a major route into the nucleus. rpL12 specifically and directly interacted with importin 11 in vitro and in vivo. Both rpL12 binding to and import by importin 11 were inhibited by another importin 11 substrate, UbcM2, indicating that these two cargoes may bind overlapping sites on the transport receptor. In contrast, the import of rpL23a, a ribosomal protein that uses the general ribosomal protein import system, was not competed by UbcM2, and in an in vitro binding assay, importin 11 did not bind to the nuclear localization signal of rpL23a. Furthermore, in a transient transfection assay, the nuclear accumulation of rpL12 was increased by coexpressed importin 11, but not by other importins. These data are consistent with importin 11 being a mediator of rpL12 nuclear import. Taken together, these results indicate that rpL12 uses a distinct nuclear import pathway that may contribute to a mechanism for regulating ribosome synthesis and/or maturation.
authors.affiliation: Center for Cell Signaling and Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908, USA. smp5g@virginia.edu
authors.forename: Scott M
authors.initials: SM
authors.lastname: Plafker
authors.forename: Ian G
authors.initials: IG
authors.lastname: Macara
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000818:Animals; D002460:Cell Line; D049452:Green Fluorescent Proteins; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism*; D008164:Luminescent Proteins / Q000378:metabolism; D051379:Mice; D008845:Microinjections; D009687:Nuclear Proteins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012269:Ribosomal Proteins / Q000378:metabolism*; D014162:Transfection; D020798:Two-Hybrid System Techniques; D020931:ran GTP-Binding Protein / Q000378:metabolism
chemical_list: D028884:Karyopherins; D008164:Luminescent Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D012269:Ribosomal Proteins; C447842:Rpl12 protein, mouse; C486193:Rpl23 protein, mouse; D049452:Green Fluorescent Proteins; D020931:ran GTP-Binding Protein