. 23. Emission spectra were analyzed with a Fluorolog 2 spectrophotometer controlled by Datamax 2.2 ( Jobin Yvon Spex) and the Grams 3.04 II software package (Galactic Industries, Salem, NH ). Both excitation and emission slits were set at 2 nm and voltage at 950 V. 24. Recombinant S-tagged Ran (2 M) preloaded with either GTP or GDP was incubated with 4 M purified YRC in phosphate-buffered saline on ice for 30 min. The Ran-GTP reaction was split into two aliquots, and one sample was treated with 100 ng of recombinant Ran-GAP. S-tagged importin  (2 M) was incubated with recombinant importin ␣ or YIC (each at 2 M final concentration) in either the presence or absence of Ran preloaded with GTP (4 M). Proteins bound to Ran or importin  were retrieved on protein-S-agarose beads, eluted with sample buffer, and analyzed by SDS-polyacrylamide gel electrophoresis (SDS-PAG
