title: Nuclear import time and transport efficiency depend on importin beta concentration.
abstract: Although many components and reaction steps necessary for bidirectional transport across the nuclear envelope (NE) have been characterized, the mechanism and control of cargo migration through nuclear pore complexes (NPCs) remain poorly understood. Single-molecule fluorescence microscopy was used to track the movement of cargos before, during, and after their interactions with NPCs. At low importin beta concentrations, about half of the signal-dependent cargos that interacted with an NPC were translocated across the NE, indicating a nuclear import efficiency of approximately 50%. At high importin beta concentrations, the import efficiency increased to approximately 80% and the transit speed increased approximately sevenfold. The transit speed and import efficiency of a signal-independent cargo was also increased by high importin beta concentrations. These results demonstrate that maximum nucleocytoplasmic transport velocities can be modulated by at least approximately 10-fold by the importin beta concentration and therefore suggest a potential mechanism for regulating the speed of cargo traffic across the NE.
authors.affiliation: Department of Molecular and Cellular Medicine, The Texas A&M University System Health Science Center, College Station, TX 77843, USA.
authors.forename: Weidong
authors.initials: W
authors.lastname: Yang
authors.forename: Siegfried M
authors.initials: SM
authors.lastname: Musser
mesh_terms: D021581:Active Transport, Cell Nucleus; D002467:Cell Nucleus / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D006868:Hydrolysis; D008856:Microscopy, Fluorescence; D019913:Nuclear Localization Signals / Q000235:genetics; D022022:Nuclear Pore / Q000737:chemistry / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D028961:beta Karyopherins / Q000378:metabolism*; D020931:ran GTP-Binding Protein / Q000032:analysis / Q000378:metabolism
chemical_list: D019913:Nuclear Localization Signals; D011993:Recombinant Fusion Proteins; D028961:beta Karyopherins; D049452:Green Fluorescent Proteins; D006160:Guanosine Triphosphate; D020931:ran GTP-Binding Protein