title: Nuclear export pathways of tRNA and 40 S ribosomes include both common and specific intermediates.
abstract: Different classes of RNAs are exported from Xenopus laevis oocyte nuclei by facilitated pathways. We have performed kinetic competition analyses to investigate the relationship between the export pathways of microinjected tRNA and ribosomal subunits. Saturating concentrations of ribosomal subunits do not compete tRNA export. Thus, the saturable factor in the ribosomal subunit export pathway is not limiting for tRNA export. The co-microinjection of ribosomal subunits did, however, stimulate the rate of tRNA export. Co-injected mRNA also stimulated tRNA export. tRNA export itself displays positive cooperative export kinetics that are abrogated by saturating concentrations of rRNA. These results are consistent with the existence of common high affinity RNA-binding sites that can be titrated with tRNA, rRNA or ribosomal subunits, and mRNA. Furthermore, high concentrations of tRNA are also shown to have moderate inhibitory effects on 40 S subunit export, indicating a lower affinity common intermediate also shared by mRNA.
authors.affiliation: Department of Biology, University of Rochester, New York 14627.
authors.forename: N J
authors.initials: NJ
authors.lastname: Pokrywka
authors.forename: D S
authors.initials: DS
authors.lastname: Goldfarb
mesh_terms: D000818:Animals; D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000378:metabolism; D012343:RNA, Transfer / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D012335:RNA, Ribosomal; D012269:Ribosomal Proteins; C086117:Rpsa protein, rat; D012343:RNA, Transfer