The compositional transition between the genomes of cold- and warm-blooded vertebrates: codon frequencies in orthologous genes |
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Authors: | Cruveiller S D'Onofrio G Bernardi G |
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Affiliation: | Laboratorio di Evoluzione Molecolare, Stazione Zoologica Anton Dohrn, Villa Comunale, I-80121, Naples, Italy. |
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Abstract: | The genomes of the ancestors of mammals and birds underwent a compositional change in which the gene-richest regions increased their GC levels. Here we investigated this compositional transition by analyzing the levels of G and C in third codon positions, as well as the codon frequencies of orthologous genes from human, chicken and Xenopus. The results may be summed up as follows: (i) GC-poor genes, that did not undergo the compositional transition, showed only minor differences in orthologous sets from Xenopus, human and chicken; this is remarkable in view of the very many nucleotide substitutions that occurred over the long evolutionary times separating these species; (ii) GC-rich genes, that underwent the compositional transition, showed large differences between Xenopus and warm-blooded vertebrates, but not between chicken and human. In other words, the independent changes that occurred in avian and mammalian genes, on the average, were the same. |
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