Construction of recombinant PRV SA215/VP2. The PRV SA215 genomic DNA was approximately 150 kb including a unique long region (UL), a unique short region (US), internal repeat (IR) and terminal repeat (TR). The thymidine kinase gene (TK) was partially deleted. PRV SA215/VP2 was generated from PRV SA215/VP2. The LacZ expression cassette was replaced with the EGFP/VP2 expression cassette by homologous recombination.