FIG. 1.

Structures of carrier complexes with Ran (A), the N-terminal domain of importinα (IBB domain) (B), and a bipartite NLS (C). H1 to H18 identify the HEAT motifs of transportin1 and importinβ. L7 is the loop within HEAT motif7. Ran (bound to GppNHp, a nonhydrolyzable analogue of GTP), the IBB domain, and the NLS are shown in white. Note how the HEAT motifs H11 to H18 are twisted up and around the IBB domain, compared to their positions in panel A (39, 263). A1 to A10 identify the ARM motifs, which are closely related to HEAT motifs. Note that the superhelical twist is in the same direction in all three structures and that the ligands all interact with the concave inner surface of the carriers.