Unique Motif for Nucleolar Retention and Nuclear Export Regulated by Phosphorylation

Abstract

By microinjecting purified glutathione S-transferase linked to all or parts of herpes simplex virus type 1 US11 protein into either the nucleus or the cytoplasm, we have demonstrated that this nucleolar protein exhibits a new type of localization signal controlling both retention in nucleoli and export to the cytoplasm. Saturated mutagenesis combined with computer modeling allowed us to draw the fine-structure map of this domain, revealing a new proline-rich motif harboring both activities, which are temperature dependent and regulated by phosphorylation. Finally, crossing the nuclear pore complex from the cytoplasm to the nucleus is an energy-dependent process for US11 protein, while getting to nucleoli through the nucleoplasm is energy independent.

We thank R. Grantham for critical reading of the manuscript and Y. Munari-Silem for generous advice on microinjection experiments.

This work was supported by the Institut National de la Santé et de la Recherche Médicale and by grants from the Association Nationale de Recherches sur le SIDA. F.C. was supported by a fellowship from the Ministère de l'Enseignement Supérieur et de la Recherche.