Genbank accession numbers for sequences from all four groups of flaviviruses (TBFV, MBFV, NKV and PABV) used for in silico analysis are listed in Supplementary  Table S1 . RNA nucleotide sequences were aligned using ClustalX (29) and then edited manually. Nucleotide and dinucleotide scans and analysis of suppression of synonymous site variability (SSSV) were determined by mean pair-wise distance comparison at each codon within the ORF using the Simmonics 1.6 package (http://www.picornavirus.org/), as previously described (30) . SSSV was calculated only at aligned codon positions in which over 40% of sequence comparisons were synonymous and averaged over a sliding window of 21 codons; consequently, data point are only produced from codon 11.