ATP-Induced Shape Change of Nuclear Pores Visualized with the Atomic Force Microscope |
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Authors: | A Rakowska T Danker SW Schneider H Oberleithner |
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Institution: | (1) Department of Physiology, University of Münster, Robert-Koch-Str. 27a, D-48149 Münster, Germany, DE |
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Abstract: | Bidirectional transport of molecules between nucleus and cytoplasm through the nuclear pore complexes (NPCs) spanning the
nuclear envelope plays a fundamental role in cell function and metabolism. Nuclear import of macromolecules is a two-step
process involving initial recognition of targeting signals, docking to the pore and energy-driven translocation. ATP depletion
inhibits the translocation step. The mechanism of translocation itself and the conformational changes of the NPC components
that occur during macromolecular transport, are still unclear. The present study investigates the effect of ATP on nuclear
pore conformation in isolated nuclear envelopes from Xenopus laevis oocytes using the atomic force microscope. All experiments were conducted in a saline solution mimicking the cytosol using
unfixed nuclear envelopes. ATP (1 mm) was added during the scanning procedure and the resultant conformational changes of the NPCs were directly monitored. Images
of the same nuclear pores recorded before and during ATP exposure revealed dramatic conformational changes of NPCs subsequent
to the addition of ATP. The height of the pores protruding from the cytoplasmic surface of the nuclear envelope visibly increased
while the diameter of the pore opening decreased. The observed changes occurred within minutes and were transient. The slow-hydrolyzing
ATP analogue, ATP-γ-S, in equimolar concentrations did not exert any effects. The ATP-induced shape change could represent
a nuclear pore ``contraction.'
Received: 10 February 1997/Revised: 10 February 1998 |
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Keywords: | : Nuclear pore complexes — ATP — Atomic force microscopy — Nuclear pore conformation |
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