Related Experiment Video
Updated: Jun 3, 2026

Single-Molecule Imaging of Nuclear Transport
Published on: June 9, 2010
Importazole, a small molecule inhibitor of the transport receptor importin-β
Jonathan F Soderholm1, Stephen L Bird, Petr Kalab
1The Department of Molecular and Cell Biology, University of California, Berkeley, MC 3200 LSA, Berkeley, California 94720-3200, United States.
Abstract:
During interphase, the transport receptor importin-β carries cargoes into the nucleus, where RanGTP releases them. A similar mechanism operates in mitosis to generate a gradient of active spindle assembly factors around mitotic chromosomes. Importin-β and RanGTP have been implicated in additional cellular processes, but the precise roles of the Ran/importin-β pathway throughout the cell cycle remain poorly understood. We implemented a FRET-based, high-throughput small molecule screen for compounds that interfere with the interaction between RanGTP and importin-β and identified importazole, a 2,4-diaminoquinazoline. Importazole specifically blocks importin-β-mediated nuclear import both in Xenopus egg extracts and cultured cells, without disrupting transportin-mediated nuclear import or CRM1-mediated nuclear export. When added during mitosis, importazole impairs the release of an importin-β cargo FRET probe and causes both predicted and novel defects in spindle assembly. Together, these results indicate that importazole specifically inhibits the function of importin-β, likely by altering its interaction with RanGTP. Importazole is a valuable tool to evaluate the function of the importin-β/RanGTP pathway at specific stages during the cell cycle.
Related Concept Videos
Nuclear Localization Signals and Import
ABC Transporters: Importer
In bacteria, based on the number of transmembrane helices and the chemical nature of their substrates, the ABC importers can be divided into three types:
Carrier-Mediated Transport
Active transport involves two types of membrane-spanning transporters: uptake and efflux. Uptake transporters are expressed in the small...
Nuclear Export
NES are of three types- the canonical 10-residue long leucine-rich signal and other...
Mitochondrial Protein Sorting
Most of these mitochondrial proteins are encoded by the nucleus and imported to the mitochondria as unfolded or loosely folded precursors. Mitochondrial precursors...
Protein Transport into the Inner Mitochondrial Membrane
Transport of mitochondrial precursors across the TIM23 channel is driven by...
