NOA36 Protein Contains a Highly Conserved Nucleolar Localization Signal Capable of Directing Functional Proteins to the Nucleolus, in Mammalian Cells

de Melo, Ivan S.; Jimenez-Nuñez, Maria D.; Iglesias, Concepción; Campos-Caro, Antonio; Moreno-Sanchez, David; Ruiz, Felix A.; Bolívar, Jorge

Three different domains can be deduced in the NOA36 protein: a poly-acidic region at the carboxy-terminus, a long cysteine-rich domain, and an amino-terminal with a high proportion of basic amino acids. In this work, we demonstrate that the NoLS of NOA36 is located at the astonishingly well-conserved N-terminus of the protein, and that a sequence of three residues of the basic amino acid lysine is critical for its nucleolar localization. In addition, we also found that this peptide is able to target the functional heterologous expression of cytosolic yeast exopolyphosphatase scPPX1 inside the nucleolus of mammalian cells. This enzyme degrades specifically inorganic polyphosphate, a compound that has been recently associated with the nucleolar transcription [39] .