Codon usage bias amongst plant viruses.

An internet database (DPVweb) was established containing details of all sequences of viruses, viroids and satellites of plants that are complete or that contain at least one complete gene (n>4600). The start and end positions of each feature (genes, non-translated regions etc) were recorded and checked for accuracy. Client software was written to enable easy selection of sequences and features of a chosen virus and to analyse codon usage bias. Codon usage was analysed for each gene of one example of each fully-sequenced plant virus. There were large differences in codon preferences, related to the nucleotide composition of the genome, particularly the GC content of the third codon position. There was no effect of gene size on codon bias. Genes from the same genome usually had similar coding strategies except where constrained by the overlap of reading frames. Although some synonymous codons were consistently used with low frequency by both plants and viruses, viruses were not generally adapted to use (or avoid) those codons most frequently used by their host plants and there was no obvious association with the type of transmission. Mutational bias, rather than translational selection appears to account for the majority of the variation detected. The software is available at http://www.dpvweb.net/analysis/codons.php.