Identification of a Short Basic Peptide Motif Able to Drive Copy-Number Dependent Nuclear Accumulation of a Linked Protein

The repetitive [RTRG]6 peptide was fortuitously identified as a potent nuclear localization signal when linked to the green fluorescent reporter protein. Replacing the arginines by lysines, or the threonines by glycines, both resulted in a decreased nuclear targeting ability of the peptide within this context. By contrast, the sequence [RT]12 proved able to drive nuclear accumulation of the linked protein as efficiently as the starting peptide. Remarkably, [RTRG]n peptides where n=2 to 6 showed a gradual, copy-number dependent, increase in their ability to target the green fluorescent protein to the cell nucleus. As a consequence, the nuclear to cytoplasmic concentration ratio of the linked protein within the cell could be adjusted to different values depending on the number of repeats used in the fusion. Our observation may open the way to the use of [RTRG]n repeats of given lengths (n=2 to 6) for fixing the nuclear-cytoplasmic partition of shuttling protein domains in the course of their functional study.