Translational selection on codon usage in Xenopus laevis.

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