Figure 4.

RanBP1 completely abolishes RanGTP binding to Nup-358–1 whereas inhibition of RanGDP binding requires both zinc chelation and RanBP1. Binding reactions with Nup-358–1 immobilized on beads were carried out as in Fig. 3 but with [β-³²P]RanGDP or [γ-³²P]RanGTP. (A) Nup-358–1, either untreated or EDTA-treated (see Materials and Methods), was incubated with [γ-³²P]RanGTP in the presence or absence of 4 μM RanBP1. (B) Binding assays were performed as in A except that [β-³²P]RanGDP was used instead of [γ-³²P]RanGTP. Bound radioactivity was measured and expressed as a percentage of total Ran-associated radioactivity in the reaction.