Evolution and revolutions of nuclear chaperones in chromatin remodeling: the nucleophosmin- nucleoplasmin family

摘要

The proper assembly of basic proteins with nucleic acids is a reaction that must be facilitated to prevent protein aggregation and formation of nonspecific nucleoprotein complexes. The proteins that mediate this orderly protein assembly are generally termed molecular (or nuclear) chaperones. The nucleophosmin-nucleoplasmin (NPM) family of molecular chaperones encompasses members that are ubiquitously expressed in many somatic tissues (NPM1 and NPM3) or specific to oocytes and eggs (NPM2). Although the study of this family of molecular chaperones has experienced a renewed interest in the last few years, information regarding the molecular evolution of these proteins is lacking. The present work shows that this family has been subject to strong purifying selection at the protein level. In contrast to NPM1 and NPM-like proteins in invertebrates, NPM2 and NPM3 have a polyphyletic origin. Furthermore, the presence of selection for high frequencies of acidic residues, as well as the existence of higher levels of codon bias, was detected at the C-terminal ends, which can be ascribed to the critical role played by these residues in constituting the acidic tracts and to the preferred codon usage for phos-phorylatable amino acids at these regions.