Schematic presentations of miRNA targeting sequences and miRNA expression cassette. (A) The FMDV genome contains a unique open reading frame. The black arrows underneath indicate the sites targeted by miRNAs. (B) Pre-miRNA oligonucleotides corresponding to each of the target sequences in 3D was inserted under the control of Pcmv and a transcriptional termination signal (TK pA). As a result, the pre-miRNA forms an intramolecular stem-loop structure similar to the structure of endogenous pre-miRNA that is processed by the endogenous Dicer enzyme into a 22 nt mature miRNA.