Fig. 5. Nuclear import of importin α is saturable but does not compete with importin β. Digitonin-permeabilized MDBK cells were incubated with 2.5 µM GFP–importin α (mRch1) alone, or 2.5 µM GST–NLS–GFP with Ehrlich ascites tumor cells cytosolic extracts and ATP regeneration system, in the presence of an excess (∼10×) amount of untagged importin α (mRch1), or 25 µM importin β mutant (1–449 amino acids) for 20 min at 30°C.