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Nucleolin, a major conserved multifunctional nucleolar phosphoprotein of proliferating cells

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Author(s): Francisco Javier Medina | Fernando Gonzalez-Camacho | Ana Isabel Manzano | Antonio Manrique | Raul Herranz

Journal: Journal of Applied Biomedicine
ISSN 1214-021X

Volume: 8;
Issue: 3;
Start page: 141;
Date: 2010;
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Keywords: ribosome biogenesis | pre-rRNA processing | protein kinases | cell cycle | prenucleolar bodies | auxin

ABSTRACT
Nucleolin is the major nucleolar protein of animal, plant and yeast proliferating cells. It is enriched in the mostsoluble nuclear or nucleolar protein extract, containing ribonucleoproteins, from which it has been purified.It has a tripartite structure in which each domain accounts for different functions. Despite itsmultifunctionality, the best characterized role of nucleolin is in the primary cleavage of pre-rRNA, an earlystep of ribosome biogenesis. In the nucleolus of proliferating cells, nucleolin is mostly located in the densefibrillar component, following a vectorial pattern, from the periphery of fibrillar centers outwards. This patternis lost in quiescent cells in which nucleolin is present in low levels. Nucleolin is the most phosphorylatedprotein of the soluble nuclear extract. It is phosphorylated by casein kinase II and CDKA, andphosphorylation is closely associated with the role of nucleolin in proliferating cells. During mitosis, nucleolinis transported from the mother to the daughter cell nucleolus in the form of processing particles, together withpre-rRNA precursors and other nucleolar proteins. It forms part of prenucleolar bodies and plays a role innucleologenesis. Recent studies on the nucleolin function, carried out on samples with inactivated nucleolingenes (siRNA downregulated or mutants) have evidenced that nucleolin is absolutely essential for cellproliferation, for the organization of the nucleolus and for transcription and processing of pre-rRNA. In plants,nucleolin controls the auxin responsiveness, thus being involved in the regulation of plant development.
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