The observation that recombinant RNAs were detected when the 2b gene of Q-CMV was substituted by that of TAV (Figure 2A , lane 9), and not when the 2b gene of Q-CMV was present in the interspecific hybrid virus C1C2T3 (Figure 2A , lane 11) suggested that the 2b gene has some role in the generation and/or selection of the recombinant viruses. However, as the replacement of the 2b sequence also changed the sequences encoding the C-terminal 41 amino acids of the 2a protein, it cannot be ruled out that the C-terminal 41 amino acids of the 2a protein might play a role in the recombination and/or selection. Therefore, to determine whether the C-terminal 41 amino acids of the 2a protein encoded by the overlapping TAV 2a gene sequence had such a role, we introduced a stop codon upstream of the TAV 2b gene in C2 T2B to prevent the expression of the C-terminal 41 amino acids of the 2a protein (see C2 T2BC2a in Figure 1 ). Bioassay of C1C2 T2BC2a T3 onto N. glutinosa showed that the virus induced symptoms similar to those induced by C1C2 T2B T3 and northern blot hybridization and RT-PCR analyses showed that recombinant RNA 3 still accumulated in the multiple passage plants, but not in the inoculated plants (data not shown). Moreover, the recombinant RNA 3 generated was the same as that derived from C1C2 T2B T3 (data not shown). Therefore, the C-terminal 41 amino acids of the 2a protein encoded by the TAV 2b sequence had no role in the recombination and/or selection, indicating that the TAV 2b gene was required for the recombination and/or selection.