To determine the nature of the recombinant RNAs derived from C1C2 W2B T3, the recombinant RNA 3 was subjected to RT-PCR, cloning and sequence analysis. Surprisingly, the RNA 3 recombinants derived from C1C2 W2B T3 differed from those derived from C1C2 T2B T3 or C1C2 T2BC2a T3 in the following respects: First, the recombinant RNA 3 derived from C1C2 W2B T3 was 22 nt longer than that derived from C1C2 T2B T3 or C1C2 T2BC2a T3 (2392 versus 2370). Second, the 3 0 terminal NTR of the recombinant RNA 3 derived from C1C2 W2B T3 contained a Q-CMV RNA 2 NTR sequence, rather than the Q-CMV RNA 1 NTR sequence (compare Figure 3A right and B right) . Third, the crossover sites on RNA 2 and on RNA 3 were different in the recombinant RNA 3 derived from C1C2 W2B T3 versus either C1C2 T2B T3 or C1C2 T2BC2a T3 (compare Figure 3A and B). And fourth, the recombinant RNA 3 derived from C1C2 W2B T3 contained an imperfect repeat of 19 nt near the crossover site preceded by an A between the TAV RNA 3 sequence and the 3 0 CMV RNA sequence ( Figure 3B) . Moreover, the recombinant RNA 3 derived from C1C2 W2B T3 also was missing the second 163-nt repeat. These similarities on one hand and differences on the other suggested that the recombinant RNA 3s derived from C1C2 T2B T3 and C1C2 T2BC2a T3 versus C1C2 W2B T3 might be generated using different templates, but occurred via a similar mechanism. Taken together, the above results indicate that the 2b protein determined either the RNA species participating in the recombination and the crossover site, or selected for particular recombinant RNAs generated at random that have the above characteristics.