The C protein of flaviviruses is highly basic at the N-terminus, specifically binding virus genomic RNA during encapsidation and plausibly acting as an RNA chaperone as shown for other viruses (58) . The sequence of SL6 within the C coding region localizes to the junction of the positively charged domain and a following hydrophobic domain that interacts with the virus envelope proteins during assembly (42) . It is possible that additional synonymous codon flexibility may be accommodated in this region due to the requirement to conserve the charge or hydrophobic characteristics of the domain, rather than any specific amino acid sequence.