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Nuclear import time and transport efficiency depend on importin ß concentration

Department of Molecular and Cellular Medicine, The Texas A&M University System Health Science Center, College Station, TX 77843

Correspondence to Siegfried M. Musser: smusser{at}tamu.edu

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 ß concentrations, about half of the signal-dependent cargos that interacted with an NPC were translocated across the NE, indicating a nuclear import efficiency of 50%. At high importin ß concentrations, the import efficiency increased to 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 ß concentrations. These results demonstrate that maximum nucleocytoplasmic transport velocities can be modulated by at least 10-fold by the importin ß concentration and therefore suggest a potential mechanism for regulating the speed of cargo traffic across the NE.

Abbreviations used in this paper: FG, phenylalanine-glycine; GMP-PNP, guanosine 5'-(ß--imido)-triphosphate; IC, import complex; NE, nuclear envelope; NPC, nuclear pore complex; SMF, single-molecule fluorescence.

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