Application of genome sequence information in potyvirus taxonomy: an overview.

The application of protein and nucleic acid sequence analysis in evolutionary and phylogenetic studies is well established. Available sequence information for the 5' untranslated region of potyviruses including the fungus-transmitted barley yellow mosaic virus (BaYMV) RNA-1 suggests that a 12-nucleotide conserved sequence, the "potybox" is unique to this group. Various non-structural proteins of potyviruses share considerable "signature" sequence homology across a broad spectrum of unrelated viruses, which makes their value limited to "supergroup" or "superfamily" identity. However, in potyviruses, the coat-protein N-terminal sequences and 3' noncoding regions are variable among viruses, but similar among strains of the same virus. This suggests that these sequences may be an accurate marker of genetic relatedness. Until complete genome sequences from a large number of potyviruses become available and their value in systematics is tested, coat protein and 3' noncoding regions remain as the choice of taxonomic indicators. The reason being, that cloning and sequencing of the coat-protein gene and 3' noncoding regions are less complicated and time consuming and the sequences show significant differences among the virus species within the family Potyviridae.