Fig. 4. Imp13 mediates import of the RBM8–MGN complex. (A) An E.coli lysate with recombinant Imp13 was used as the starting material for the binding experiment. Imp13 bound very efficiently and in a RanGTP-sensitive manner to immobilized RBM8 and the RBM8–MGN complex. (B) Binding was performed as in (A), except that MGN was immobilized instead of RBM8. Imp13 bound only weakly to MGN alone, but efficiently to the MGN–RBM8 complex. (C) A pre-formed RBM8–MGN complex was fluorescently labelled and used at 1 µM as an import substrate as described in Figure 3. Import was efficient with Imp13 and hardly detectable with any other nuclear transport receptor (each used at 2 µM).