The recombinant RNA 3 derived from C1C2 W2B T3 Á163(A) consisted of the 5 0 proximal 2082 nt from TAV RNA 3 and the 3 0 proximal 309-nt 3 0 NTR of CMV RNA 2 ( Figure 5C ). Although the 2082 nt sequence from TAV RNA 3 was exactly the same as that in the recombinant RNA 3 derived from C1C2 T2B T3 Á163(A) , it was 18 nt longer than the one seen in the recombinant RNA 3 derived from C1C2 W2B T3 (compare Figures 3B  and 5C ). This result supports the conclusion that the first 163-nt repeat might indeed affect the left border of the crossover site. The CMV RNA 2 sequence present in the recombinant RNA 3 derived from C1C2 W2B T3 Á163(A) was 19 nt shorter than the CMV RNA 2 present in the recombinant RNA 3 derived from C1C2 W2B T3 (due to the absence of the additional A and the first 19-nt repeat shown in Figure 3B , but with an additional U residue, nucleotide 2757), suggesting that the first 163-nt repeat might also affect the right border of the crossover site. In the recombinant RNA 3 derived from C1C2 W2B T3 Á163(G) , the sequence was exactly the same as that of the recombinant RNA 3 derived from C1C2 W2B T3 (compare Figures 3B and 5D) , confirming that the second 163-nt repeat had no role in determining the position of the crossover sites on either RNA. Since only one nucleotide differed in the two 163-nt repeats (A versus G), the above results indicate that the position of the crossover sites is actually affected by this single nucleotide difference within each repeat.