Seven different human Importins bind the H3 and H4 tails.
A, domain organization of human histones H3 and H4. B, pulldown binding assays of immobilized GST-H3 tail and GST-H4 tail (each 20 nmol; 250 nm) with a 500 nm concentration of each Importin (SDS-PAGE/Coomassie Blue). Relative densities of the gel bands from three separate experiments are plotted in histograms. One-way ANOVA tests were performed (H3 tail, p < 0.0001; H4 tail, p < 0.0001). Error bars represent S.D. C, Impα binding to immobilized GST-SV40 c-NLS, GST-H3 tail, and GST-H4 tail. Impα binds more tightly to the c-NLS than to the histone tails. D, binding assays of immobilized GST-H3 tail with Impβ, Kapβ2, Imp4, Imp5, Imp7, and Imp9 in the presence and absence of RanGTP (SDS-PAGE/Coomassie Blue). E, control experiments. Left panel, input samples of purified recombinant Importins (5 μl; 8 μm concentration of each protein; ∼10% of proteins used in B and in Figs. 2; 3C; 4, B–D; 5; and 6). Middle panel, Importin (∼4 μm) binding to GST protein (0.8 nmol; ∼2 μm) immobilized on glutathione-Sepharose. Right panel, Importin binding to immobilized GST-RanGTP. All six β-Importins bind RanGTP tightly.