The above results showed that the CMV sequence in the recombinant RNA 3 was similar or identical to the CMV RNA 5 sequence. Correspondingly, the TAV RNA 3 sequence in the same recombinant RNA 3s lacked the second 163-nt repeat and the rest of the 3 0 NTR (which together corresponds to the TAV RNA 5 sequence). To determine whether CMV RNA 5 itself or the 3 0 NTR of CMV RNAs 1 and/or 2 could be used as a template for the synthesis of the recombinant RNA 3, we prepared the appropriate templates that would be expressed transiently in inoculated plants and assessed these for the presence of recombinant virus. In the templates, we deleted 326 nt from the 3 0 NTR of T3 to make T3 , and deleted the first 163-nt repeat plus 141 nt from the 3 0 NTR of T3 to make T3 Á163(A)Á141 (Figure 1 ). These two deletions had the same length of the TAV RNA 3 sequence as in the recombinant RNAs. In addition, we also made four RNA 5-like cDNA clones, C1 3081-3390 , C2 W2B2757-3065 , T3 1902-2386 and T3 2065-2386 . The former two were based on the CMV RNA 1 and C2 W2B sequences in the recombinant viruses, respectively, while the latter two were based on the sequence of TAV RNAs 3B and 5, respectively (39) . All of these clones were placed into the pCass1 vector, under transcriptional control of the CaMV 35S RNA promoter and terminator sequences. The infectivity results of the various plasmid mixtures tested on N. glutinosa and N. clevelandii plants are shown in Table 1 (Table 1 ). These results indicate that the sequences containing the 3 0 NTR are essential for the viral infection and could not be separated functionally from the rest of the TAV RNA 3 sequence. In addition, the results also indicate that the recombination observed in other experiments did not occur during the synthesis of (À) sense RNA from (+) sense templates, since there was no repair of the 3 0 NTR from synthesis initiated on either genomic RNAs 1 or 2, or subgenomic RNAs 3B or 5 (Table 1) and template switching to TAV RNA 3 lacking the 3 0 NTR. Such repair recombination is common among tombusviruses (8, 53) and occurs with the related brome mosaic virus (54) (55) (56) . Therefore, an alternative explanation is that the recombination occurred during (+) sense RNA synthesis on the (À) sense RNA templates, with recombination occurring as a result of template switching of the viral replicase from the donor (TAV RNA 3) strand to the acceptor (CMV RNA) strand.