Ran(T24N) binding triggers a conformational switch in the RCC1 tail. (A) Ran(T24N) decreases FRET efficiency of the RCC1 biosensor. Emission spectra are shown ± recombinant Ran(T24N), with excitation at 430 nm. (B) Titration of FRET efficiency with increasing Ran(T24N) concentration. (C) GTP-bound Ran(Q69L) does not change FRET efficiency. Emission spectra were obtained ± recombinant Ran(Q69L) and ± GTP and Mg²⁺. (D) Quantification of YFP/CFP emission ratio at different concentrations of Ran(Q69L) in the presence or absence of GTP and Mg²⁺. Emission efficiencies are compared with those in the presence of equivalent concentrations of Ran(T24N). (E) Core histones increase FRET efficiency. Emission spectra are shown ± purified core histone octamer. (F) Titration of YFP/CFP emission ratio with increasing concentrations of core histones. (G) Ran(T24N) can still decrease FRET efficiency even in the presence of histones. Recombinant Ran(T24N) was added after the addition of histones. (H) Quantification of emission ratios (YFP/CFP) when titrating with Ran(T24N) in the presence of histones. Error bars represent ±1 SD.