BIOCHEMISTRY: Through the Isinglass

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Science  30 Mar 2001:
Vol. 291, Issue 5513, pp. 2519c
DOI: 10.1126/science.291.5513.2519c

The nuclear pore complex (NPC) is embedded in the nuclear envelope and enables transport between the nucleus and the cytoplasm. Small molecules can diffuse through the pore, but larger molecules must be bound by nuclear transport receptors that facilitate transport through interaction with the NPC.

Ribbeck and Görlich have measured translocation rates and capacities for various model substrates. They find that the NPC is capable of about 1000 translocations per second, corresponding to a mass flux of about 100 megadaltons per second. The affinity of the substrates for NPC components is low and consistent with micromolar affinities measured previously for interactions between substrates and the phenylalanine-rich nucleoporin repeats, which have been implicated in translocation. These repeats are thought to be a major constituent of the central plug, a material of low electron density that fills the pore of the NPC. The authors suggest that these repeats form a sieve-like structure that restricts the flow of large molecules unless they can compete for direct binding to the motifs. Weak interactions of these motifs with nuclear transport receptors would allow infiltration of the barrier and facilitate fast transport. — VV

Acknowledgments

EMBO J. 20, 1320 (2001).

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