Two other mutants C27 and C34 had shortened stems due to the formation of a large internal bulge (Figure 4) , and exhibited profoundly altered biological characteristics (Table 1 and Figure 5 ). However, C27 and C34 included amino acid substitutions Q 28 !N and Q 28 !P, respectively, the latter resembling POWV (Figure 3 ). To rule out the amino acid change as influential, two mutants were designed as a control for C27; double mutant N 28 V 39 and single mutant V 39 , neither of which affected SL6 conformation (Figure 4 ). Similarly mutant P 28 , a control for C34, contained the same amino acid substitution Q 28 !P but maintained SL6 conformation (Figures 3  and 4 ). All three control mutants, N 28 V 39 , V 39 and P 28, displayed wild-type large plaque phenotype and cpe (Table 1) .