UPMGA analysis of WNV genomes. The image summarizes the results of the bioinformatics analysis. Some reference strains are shown. Sequence alignment identifies WARF4 in 98% of strain belonging to lineage I (black collapsed form). The WARF4 group (dashed) may be further separated in two groups, depending on the type of programmed −1 ribosomal frame shifting sequence detected. Group 1 carries the UUUUUUG slyppery sequence. Group 2 carries the CCCUUUG/T slippery sequence. The two pseudoknot sequences with the predicted base pairing are shown. The slippery sequences are in gray while the stop codon (AUG) and the first codon (GGC) of WARF4 are underlineed.