Construction and expression of vaccine plasmids. (A) A schematic representation of the recombinant vaccine plasmids. The plasmid pcDNA3.1/IL-2 was constructed by inserting the HindIII and an KpnIdigested the PCR-amplified IL-2 DNA fragment into HindIII and an KpnI sites of pcDNA3.1 (+) between the cytomegalovirus promoter sequence and the bovine growth hormone polyadenylation sequence. The plasmid pcDNA3.1/HTNV-IL-2-G2 was constructed by inserting the KpnI and XhIdigested HTNV G2 DNA fragment into the KpnI and EcoRI sites of pcDNA3.1/IL-2 plasmid upstream and in frame with the IL-2 gene. (B) Identification of recombinant plasmids by using restriction enzyme digestion and agarose gel electrophoresis. Lane M, DNA molecular size marker; lanes1–3, pcDNA3.1/HTNV-IL-2-G2 digested with HindIII and KpnI, HindIII and XhI, KpnI and XhI, respectively.