The molecular dynamics of nuclear protein import were examined in a solution binding assay by testing for interactions between a protein containing a nuclear localization signal (NLS), the transport factors karyopherin α, karyopherin β, and Ran, and FXFG or GLFG repeat regions of nucleoporins. We found that karyopherins α and β cooperate to bind FXFG but not GLFG repeat regions. Binding of the NLS protein to karyopherin α was enhanced by karyopherin β. Two novel reactions were discovered. First, incubation of a karyopherin heterodimer-NLS protein complex with an FXFG repeat region stimulated the dissociation of the NLS protein from the karyopherin heterodimer. Second, incubation of the karyopherin heterodimer with RanGTP (or with a Ran mutant that cannot hydrolyze GTP) led to the dissociation of karyopherin α from β and to an association of Ran with karyopherin β; RanGDP had no effect. We propose that movement of NLS proteins across the nuclear pore complex is a stochastic process that operates via repeated association-dissociation reactions. © 1995.
Rexach, M., & Blobel, G. (1995). Protein import into nuclei: association and dissociation reactions involving transport substrate, transport factors, and nucleoporins. Cell, 83(5), 683–692. https://doi.org/10.1016/0092-8674(95)90181-7