FIG. 1.

Schematic representation of the sequence conservation of SL2 in the CoV 5′ leader region (A), as well as cartoon renderings of a canonical UNR U-turn loop (B) and a CUUG tetraloop (C) structures, each of which is compatible with the SL2 sequence conservation of panel A. Nucleotide sequence and secondary structural models of SL2 derived from the two group 2 CoVs MHV (D) and SARS-CoV (E), which were studied here. Note that the cartoons are highly schematized; the internucleotide linkages shown are standard 5′-3′ phosphodiester linkages. The 16-nt NMR target corresponds to the SARS-CoV SL2 sequence, except that U57 is replaced with a nonnative 3′ unpaired A. See the text for details.