Response of transgenic plants expressing various N cDNA reconstructions to TMV. Primary TMV-U1 inoculated (1° I.L.) and secondary uninoculated upper leaves (2° U.I.L.) from transgenic SR1:nn plants bearing cDNA-NS:3′ GS (A), cDNA-NL:3′ GS (B), and cDNA-NS:3′ GS∷cDNA-NL:3′ GS (C), cDNA-NS + intron III (AE):3′ GS (D), and cDNA-NS + intron III (AE):NOS (E) constructions. c-DNA-NS and cDNA-NL, alternative N messages. AE, AE in intron III of the N gene. 3′ GS, 1.4-kb GS (open rectangle with zig-zags) downstream of the N gene stop codon. NOS, terminator sequences (filled black rectangle) from the NOS gene.