Fig. 1.

Predicted secondary structure model of MHV-A59 SL1 constructs discussed here. (a) WT;²⁰ (b) WT*, which corresponds to SL1-Δ(C16/C19/C20) with a 5′-GA overhang required for initiation of in vitro transcription by SP6 polymerase; and (c) second-site revertant SL1s derived from infection with the SL1-ΔA35 virus (ΔA35 RNA sequence shown; recovered single-nucleotide substitutions highlighted in red). The constructs labeled WT*, ΔA35, ΔA35/U33C, ΔA35/C34U, and ΔA35/A36U RNAs (b and c) were used for the NMR and thermal unfolding studies. The 5′ g is a non-native nucleotide, shown in lower case.