Variation in G + C-content and codon choice: differences among synonymous codon groups in vertebrate genes.

The relationship between G + C-content and codon usage in genes of human, mus, rat, bovine and chicken nuclear genomes was investigated. Correlation and lineal regression analyses were carried out on plots that related the frequency of each codon within each synonymous codon group to the G + C-content of the coding sequence as a whole. Under GC pressure, in most of the quartet codon groups there is a preferential choice of the C-ending codon, except in leucine and valine codon groups where the choice of the G-ending codon is preferred. Among ducts, the choice of codons specifying phenylalanine and glutamate shows the strongest dependence on G + C-content. The relationship found between G + C-content and codon usage in these genomes correlate with taxonomic distance.