CODON USAGE IN CAENORHABDITIS-ELEGANS - DELINEATION OF TRANSLATIONAL SELECTION AND MUTATIONAL BIASES

Synonymous codon usage varies considerably among Caenorhabditis elegan s genes. Multivariate statistical analyses reveal a single major trend among genes. At one end of the trend lie genes with relatively unbias ed codon usage. These genes appear to be lowly expressed, and their pa tterns of codon usage are consistent with mutational biases influenced by the neighbouring nucleotide. At the other extreme lie genes with e xtremely biased codon usage. These genes appear to be highly expressed , and their codon usage seems to have been shaped by selection favouri ng a limited number of translationally optimal codons. Thus, the frequ ency of these optimal codons in a gene appears to be correlated with t he level of gene expression, and may be a useful indicator in the case of genes (or open reading frames) whose expression levels (or even fu nction) are unknown. A second, relatively minor trend among genes is c orrelated with the frequency of G at synonymously variable sites. It i s not yet clear whether this trend reflects variation in base composit ion (or mutational biases) among regions of the C. elegans genome, or some other factor. Sequence divergence between C. elegans and C. brigg sae has also been studied.