FIG. 1.

Schematic representation of BMV RNA recombination constructs and the stem-loop inserts. The top portion shows the 3′ regions of wt BMV RNA1 and -2 and the modified 3′ region of PN-H39 RNA3. The latter consists of a duplication of the tRNA-like structure sequence (regions A and B), each carrying a viable m4 deletion (represented by small rectangular boxes) and an insertion of a 765-nt 3′ fragment of CCMV RNA3 (region C; see reference 32). The recombinationally active 60-nt region R, which is homologous between RNA3 and -2, is represented by a box with the letter R, and the arrow points to the sites of the stem-loop inserts. Region D comprises the rest of the 3′ NCR (32). The large gray boxes to the left represent the open reading frames (not to scale) of protein 1a, 2a, or protein 3a and the coat protein (CP), which are encoded by RNA1, -2, and -3, respectively. The bottom portion of the figure shows computer-predicted secondary structures of the positive-strand stem-loop inserts (in bold face) that were introduced between pseudoknots pkG and pkH (27) of region R. Nucleotides in brackets represent the helix-destabilizing substitutions (in constructs 2ss+ and 3ss+). The negative-strand stem-loop inserts are not shown.