The phylogenic alignment of homologous L35 protein suggests that human large subunit ribosomal protein L35 carries a 54 aa eukaryotic expansion segment (ES) at the C-terminal end. Within this ES, the first 25 amino acid residues were found to be essential for the nuclear import of the protein. The last 29 residues of the ES were shown to be uninvolved in the ribosome's structural and translational functions, although this region proved to be one of the contact sites for ribosomal docking to endoplasmic reticulum, as evident from the results of an in vivo recombinant ribosome analysis.

Edited by Ulrike Kutay Keywords:Eukaryotic ribosomal protein L7 Importin b3 Nuclear localization signal (NLS) Biosensor Overlay assay Fluorescence recovery after photobleaching (FRAP) assay a b s t r a c tWe show that importin b3 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.

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