FIG. 5.

RNA secondary structure model showing the proposed SL4-SL5 pseudoknot interaction and pseudoknot mutants. The nucleotides involved in the pseudoknot interaction are marked in gray, and the base-pairing interaction is depicted by lines. The orientation of the central pentanucleotide in the loop was changed in SL4 (Or4) or SL5 (Or5) or both (Or45), which restored base-pairing possibilities. The pentanucleotide sequence of SL4 was switched with that of SL5 in mutant Sw4, and vice versa in mutant Sw5. Base-pairing possibilities were again restored in mutant Sw45. The stop codon of the N protein gene is underlined.