An in vitro binding assay established that the N-terminal domain of Nab2 interacted directly with the Mlp1 C-terminus. Recombinant proteins were expressed and purified from E. coli as described in Materials and Methods. Either GST-Nab2-N or GST control protein was incubated with the Mlp1 C-terminal domain fragment. As shown in Fig. 1d, the Mlp1 fragment bound to GST-Nab2-N but not to the control GST protein, confirming that the N-terminal domain of Nab2 interacts directly with the C-terminal domain of Mlp1. The amount of binding between Nab2-N and CT-Mlp1 appears to be substoichiometric, which is consistent with the interaction between Nab2 and Mlp1 being relatively weak, to facilitate export rather than retention at the nuclear pore. Preliminary binding studies indicated that the Kd for this interaction is in the micromolar range (data not shown).