Cloning and Sequence Analysis of ORF5 Gene of Porcine Reproductive and Respiratory Syndrome Virus of the ZJ Strain

A pair of the special primers was designed and synthesized according to the ORF5 sequence of porcine reproductive and respiratory syndrome virus (PRRSV), which was published in GenBank. In 2009 a pig farm in Zhejiang province suspected some diseased and dead pigs displaying symptoms of porcine reproductive and respiratory syndrome and provided 12 samples (spleen, kidney or lymph nodes) for laboratory diagnosis. The samples were positive of porcine reproductive and respiratory syndrome by PCR. The ORF5 gene was amplified by RT-PCR and cloned into pMD-18T vector. Nucleotide sequence was determined by sequencing and compared with other ORF5 genes in GenBank. Then, the structure of ORF5 gene was analyzed. Results showed that the amplified fragment length was 603 bp，encoding 201 amino acids. Compared with the corresponding region of other PRRSV strains, the nucleotide sequence homology was 63.5% - 90.7% with other strains published in GenBank, amino acid sequence homology was 11.2% - 87.6% and the nucleotide sequence homology was 90.7% with AF494042 strain of American type. Therefore, we suggest that the isolates of ZJ strain belong to the American type. The ORF5 gene encoding the GP5 protein is the main structure protein and immune protein, involving the generation of neutralizing antibody. Thus, GP5 has good properties as new target protein of gene engineering vaccine and diagnosis kit. This study provides valuable reference for development of a vaccine based on GP5 protein.