Isochore evolution in mammals: a human-like ancestral structure.
Codon usage in mammals is mainly determined by the spatial arrangement of genomic G + C-content, i.e., the isochore structure. Ancestral G + C-content at third codon positions of 27 nuclear protein-coding genes of eutherian mammals was estimated by maximum-likelihood analysis on the basis of a nonhomogeneous DNA substitution model, accounting for variable base compositions among present-day sequences. Data consistently supported a human-like ancestral pattern, i.e., highly variable G + C-content among genes. The mouse genomic structure-more narrow G + C-content distribution-would be a derived state. The circumstances of isochore evolution are discussed with respect to this result. A possible relationship between G + C-content homogenization in murid genomes and high mutation rate is proposed, consistent with the negative selection hypothesis for isochore maintenance in mammals.
Galtier
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N
Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5558, Biométrie, Génétique et Biologie des Populations, Université Claude Bernard Lyon 1, 69622 Villeurbanne Cedex, France.
Mouchiroud
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D
D000818:Animals; D003596:Cytosine; D019143:Evolution, Molecular; D006147:Guanine; D006801:Humans; D008322:Mammals / Q000235:genetics*; D051379:Mice; D008957:Models, Genetic; D010802:Phylogeny
D006147:Guanine; D003596:Cytosine