Importin β3 mediates the nuclear import of human ribosomal protein L7 through its interaction with the multifaceted basic clusters of L7.

We show that importin β3 is essential for the nuclear import of L7. The import is mediated via the multifaceted basic amino acid clusters present in the NH(2)-region of L7, and is RanGTP-dependent. Using a (EGFP)(3) reporter system and a FRAP assay, the role the individual clusters play as a functional NLS has been characterized, and each cluster was found to exhibit a different rate of real time nuclear uptake. We assume that having such a multiple NLS may provide L7 with preferential nuclear uptake.