That the 2b protein rather than the 2b RNA sequence itself affected the generation and/or selection of recombinant RNA 3s could not be established conclusively, since expression of the 2b gene was shown to be necessary for the cell-to-cell movement, but not the replication of the pseudorecombinant virus C1C2T3 (21) . However, if the 2b protein was actually involved in the recombination/ selection process, then at a minimum the 2b protein should be capable of binding viral RNA. To determine 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 C1C2T3 whether there was some interaction between TAV RNA 3 and the 2b protein, we performed an RNA-proteinbinding assay. The TAV 2b protein ( Figure 4B , lane 3) purified from E. coli ( Figure 4A ) was able to bind to the T7-transcribed (+) sense TAV RNA 3 ( Figure 4C , lanes 2-4) as well as to the T3-transcribed (À) sense TAV RNA 3 ( Figure 4D , lane 3). The binding ability increased with an increasing amount of the 2b protein ( Figure 4C , compare lanes 1-4). By contrast, comparable amounts of GST alone, which was expressed and purified under the same conditions as the TAV 2b protein ( Figure 4B , lane 2), did not bind to TAV RNA 3 (data not shown). This demonstrated that RNA-binding activity was not due to a co-purified, contaminating protein from E. coli. The significance of the more efficient binding of the 2b protein to (+) versus (À) sense RNA is unknown. The different binding abilities probably are due to different sequences and/or structures between RNA 3(+) and RNA 3(À). Since the 2b protein was designated a movement protein (19) and was shown to be required for the movement of pseudorecombinant viruses containing C1C2T3 (21), the 2b protein probably also binds to TAV RNA 3 in vivo.