Despite sequence divergence, all viruses in the mTBFV group formed similar SL6-like structures when the 333 nt or a longer nucleotide region (up to 1000 nt) was used for MFold analysis (data not shown). The SL6-like folds contained a remarkably high number of co-variant and semi-covariant substitutions which maintained the general conformation across divergent viruses ( Figure 1B ). The minimum free energy dG of folding for SL6 varied between À32.3 and À17.2 kcal/mol with RFV and LIV/GGYV as extremes in this range. Although KADV had a shorter SL6 compared with other TBFVs, the energy of folding was À17.32 kcal/mol, within the range found for mTBFV.