Real-time trafficking and assembly of ribosomal subunits

Abstract

Nuclear pore complexes (NPCs) facilitate the bidirectional transport of a myriad of molecules, ranging in size from an ion to assembled ribosomal subunits, across the two lipid bilayers that constitute the nuclear envelope (NE). Research over the past decade has imparted much insight into how NPCs control the selective passage of large macromolecules while maintaining their compartmentalization properties. Schemes for soluble cofactor-mediated active transport have been developed through phenotypic mutational analyses and in vitro experiments. Continuing the effort for a more comprehensive characterization of NPC function, we have developed a method for the in vivo analysis of nucleocytoplasmic transport utilizing fluorescently labeled, recombinant human ribosomal protein L23a (rpL23a-His). Cytoplasmic microinjections into live HeLa cells indicated rapid nuclear import and subsequent export of rpL23a-His. These results are expected to lead to real-time in vivo single-molecule observation of ribosomal subunit trafficking and assembly.