To characterize the RT-PCR products further, Southern blot hybridization was done using CMV-specific and TAV-specific probes. All the RT-PCR products on the gel were the same size ( Figure 6 middle and lower panels) and the size was also the same as for the RT-PCR products obtained from the passage plants (data not shown). In addition, all the RT-PCR products were able to hybridize with both the Q-CMV-specific probe and the TAV-specific probe ( Figure 6 middle and lower panels). Sequencing of these RT-PCR products showed that the RT-PCR products from the C1C2 T2B T3 Á163(G) -inoculated plants contained 874 nt derived from TAV RNA 3 (up to nucleotide 2060 of TAV RNA 3) and 310 nt from CMV RNA 1. This sequence was exactly the same as that derived from the same virus in the passage plants and also the same sequence as that derived from C1C2 T2B T3, either in the inoculated plants or in the passage plants ( Figures 3A and 5B ; data not shown). All of the RT-PCR products derived from C1C2 W2B T3 Á163(G) also were exactly the same in sequence, having 878 nt from TAV RNA 3 and 326 nt from CMV RNA 2 including the 19-nt repeat ( Figure 5D ; data not shown). The sequence of the RT-PCR products also were the same as those from the passage plants, or those derived from C1C2 W2B T3 in both the inoculated plants and passage plants ( Figure 3B ; data not shown). These results indicate that the recombinant RNA 3s accumulating in the infected plants did not contain a detectable intermediate, and that the crossover sites on both donor and acceptor RNAs occurred at the same position.