FIG. 3.

Mechanism of cargo import by the importinα-importinβ pathway. In this mechanism, the cargo binds to an adapter, importinα, rather than directly to the carrier. The cargo-importinα-importinβ complex is disassembled in the nucleus by RanGTP. Importinβ returns to the cytosol, as shown in Fig. 2. The importinα requires a carrier for export, called CAS (CseI in budding yeast). Assembly of the export complex requires RanGTP. The ternary importinα-CAS-RanGTP complex is disassembled in the cytoplasm by hydrolysis of the GTP.