Qualitative analysis of IBB peptide binding on importin α, β, and GST. Binding assays were performed between importin β-GST (Imp β) and IBB peptide (IBB) or cytochrome c (Cytc) (A and B) and between importin α-GST (Imp α), importin β-GST (Impβ), or GST and IBB peptide (C and D). Importin-GST or GST were fixed on glutathione-sepharose beads and 1.25 μg (1), 2.5 μg (2) or 5 μg (3) of IBB peptide, or 1.25 μg (4), 2.5 μg (5) or 5 μg (6) of cytochrome c were applied to these beads. The unbound (A and C) and bound (B and D) fractions were analyzed on 10 % NuPAGE gels (Invitrogen) followed by Coomassie Blue staining (A and B) or silver nitrate staining (C and D). M: protein size ladder (Novex), C1: 500 ng IBB peptide and 500 ng cytochrome c as a control, C2: 500 ng GST, 500 ng importin α and 500 ng importin β as a control.