Fig. 3. Transport receptors bind directly to SRP19 in a RanGTP-regulated manner. A GST-SRP19 fusion protein was immobilized on glutathione-sepharose and incubated with purified nuclear transport receptors, with and without RanQ69L[GTP] as described in Materials and Methods. After washing, bound proteins were eluted with SDS sample buffer and analyzed by SDS-PAGE. (A) Proteins that bound to GST-SRP19 in the presence (+) and absence (-) of RanQ69L[GTP]. Note that binding of all receptors to SRP19 was greatly reduced in the presence of RanQ69L[GTP]. (B) Purified receptors, in the same order as in A, loaded as reference samples. The asterisk indicates GST-SRP19.