We excluded the possibility that SSSV in the C-coding region was due to codon bias by analyzing nucleotide composition at each position within the codons. Comparison of SL6 between TBFV species. Numeration in brackets corresponds to SL6 numbered from the start codon of each virus (abbreviated in Table S1 ). Free energy dG values of folding are shown in kcal/mol. Covariant and semi-covariant substitutions are underlined on Vs virus.