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Nucleolins from different model organisms have conserved sequences reflecting the conservation of key cellular functions through evolution

Author(s): Fernando Gonzalez-Camacho | Francisco Javier Medina

Journal: Journal of Applied Biomedicine
ISSN 1214-021X

Volume: 2;
Issue: 3;
Start page: 151;
Date: 2004;
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Keywords: Nucleolar protein | nuclear localization sequence | RNA recognition motifs | glycin-arginin-rich | phylogenetic study | evolution

Sequences available in public protein databases belonging to nucleolin or nucleolin-like proteinshave been aligned using public domain software, in order to obtain relevant data regarding thedegree of their conservation, which could be a reflection of the degree of conservation of thefunctions currently attributed to this protein. Nucleolin is known to be a nucleolar multifunctionalprotein, involved in different steps of pre-rRNA transcription and processing. Three domains areconstantly present in all nucleolins, namely a series of acidic/serin (Ac/Ser) sequences, a number ofRNA recognition motifs (RRM) and a region rich in glycin and arginin (GAR). The number ofmotifs present in each one of the three domains is variable. Furthermore, we have characterized inall nucleolins the presence of a bipartite consensus nuclear localization sequence (NLS). The onlycases in which this sequence with a definite structure was not totally evident were in the yeastS. pombe (a possible monopartite structure) and in the protozoan T. thermophyla, in which itappears to be absent. Finally, we have constructed the phylogenetic tree of the 15 speciesinvestigated, taking exclusively the data regarding this protein. Interestingly, the tree obtainedclosely resembles the organization of these taxonomic groups throughout evolution, as it ispresently known. We conclude that nucleolin is a highly conserved protein, whose gene wasalready present in an ancestor eukaryotic species, at an early stage of the evolutionary process,from which it has evolved very slowly. This is a reflection of the fundamental functions carried outby this protein, which were already fixed in the ancestor species.
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