(A) Modified plasmids derived from pCGxAF9VP2HRT, which containing segment A of the virulent strain rGx-F9VP2 (depicted by an open box). In plasmids pCGxATA-A854GHRT, pCGxATA-A876GHRT, pCGxATA-A896GHRT, pCGxATA-G938AHRT, and pCGxATA-G965AHRT, the nucleotide substitutions A854G, A876G, A896G, G938A, and G965A resulted in the amino acid substitutions I242V, Q249R, I256V, A270T, and D279N of the VP2 protein of the virulent strain rGx-F9VP2, respectively. (B) Modified plasmids derived from pCmGtAHRT, which containing segment A of attenuated strain rGt (depicted by a box with dot). In plasmids pCmGtA-G876AHRT and pCmGtA-G896AHRT, the nucleotide substitutions G876A and G896A resulted in the amino acid substitutions R249Q and V256I in the VP2 protein of the attenuated strain rGt, respectively. The genomic cDNA sequences are preceded by a cytomegalovirus enhancer and a beta chicken actin promoter and are flanked by the cDNAs of HamRz and HdvRz. The restriction enzyme sites used for the construction of recombinant vectors are also shown.