The N gene, a member of the Toll-IL-1 homology region-nucleotide binding site-leucine-rich repeat region (LRR) class of plant resistance genes, encodes two transcripts, N S and NL, via alternative splicing of the alternative exon present in the intron III. The NS transcript, predicted to encode the full-length N protein containing the Toll-IL-1 homology region, nucleotide binding site, and LRR, is more prevalent before and for 3 hr after tobacco mosaic virus (TMV) infection. The NL transcript, predicted to encode a truncated N protein (N tr ) lacking 13 of the 14 repeats of the LRR, is more prevalent 4 -8 hr after TMV infection. Plants harboring a cDNA-NS transgene, capable of encoding an N protein but not an N tr protein, fail to exhibit complete resistance to TMV. Transgenic plants containing a cDNA-NS-bearing intron III and containing 3 Ngenomic sequences, encoding both N S and NL transcripts, exhibit complete resistance to TMV. These results suggest that both N transcripts and presumably their encoded protein products are necessary to confer complete resistance to TMV.