RNA interference (RNAi) involves the degradation of homologous mRNA sequences in organisms and is induced by double-stranded RNA (dsRNA). We have constructed three hairpin RNA (hpRNA) prokaryotic expression vectors derived from the 5' region, the middle region and the 3' region of the Nuclear inclusion protein b (NIb) gene, and then expressed these in M-JM109lacY. Resistance analyses and Northern blotting showed that different hpRNAs had different abilities to protect tobacco plants from infection with Potato virus Y (PVY) and that this resistance was RNA-mediated.