As a general strategy for constructing siRNAexpressing plasmids, inverted repeats targeting the sequence were cloned into plasmid pU6 at the EcoRI/HindIII sites, under the control of the U6 promoter and the termination signals of 4 or 5 thymidines. Plasmids p3D-NT19, p3D-NT56, pVP4-NT19, pVP4-NT65 and p2B-NT25 contained inverted repeats corresponding to the nucleotide sequences of the FMDV genome, as described below.