Translational selection on codon usage in Xenopus laevis

A correspondence analysis of codon usage in Xenopus laevis revealed that th e first axis is strongly correlated with the base composition at third codo n positions. The second axis discriminates between putatively highly expres sed genes and the other coding sequences, with expression levels being conf irmed by the analysis of Expressed sequence tag frequencies. The comparison of codon usage of the sequences displaying the extreme values on the secon d axis indicates that several codons are statistically more frequent among the highly expressed (mainly housekeeping) genes. Translational selection a ppears, therefore, to influence synonymous codon usage in Xenopus.