M. Floer et al., DISASSEMBLY OF RANGTP-KARYOPHERIN-BETA COMPLEX, AN INTERMEDIATE IN NUCLEAR-PROTEIN IMPORT, The Journal of biological chemistry, 272(31), 1997, pp. 19538-19546
We previously showed that RanGTP forms a 1:1 complex with karyopherin
beta that renders RanGTP inaccessible to RanGAP (Floer, M., and Blobel
, G. (1996) J. Biol. Chem. 271, 5313-5316) and karyopherin beta functi
onally inactive (Rexach, M., and Blobel, G. (1995) Cell 83, 683-692).
Recycling of both factors for another round of function requires disso
ciation of the RanGTP-karyopherin beta complex, Here we show using BIA
core(TM), a solution binding assay, and GTP hydrolysis and exchange as
says, with yeast proteins, that karyopherin beta and RanGTP are recycl
ed efficiently in a reaction that involves karyopherin alpha, RanBP1,
RanGAP, and the C terminus of the nucleoporin Nup1. We find that karyo
pherin alpha first releases RanGTP from karyopherin beta in a reaction
that does not require GTP hydrolysis, The released RanGTP is then seq
uestered by RanBP1, and the newly formed karyopherin alpha beta binds
to the C terminus of Nup1. Finally, RanGTP is converted to RanGDP via
nucleotide hydrolysis when RanGrAP is present, Conversion of RanGTP to
RanGDP can also occur via nucleotide exchange in the presence of RanG
EF, an excess of GDP, and if RanBP1 is absent. Additional nucleoporin
domains that bind karyopherin alpha beta stimulate recycling of karyop
herin beta and Ran in a manner similar to the C terminus of Nup1.