Abstract: In order to characterize the epidemic law of PRRS in Ningxia, the RT-PCR assay was used to amplify the cDNA fragment of ORF3 gene, a protein-encoding gene of GP3 protein, from the PRRSV clinical isolate. The results showed that the ORF3 gene of the PRRSV clinical isolate was 765 bp in length and encoded 254 amino acids. It had more than 85% homology with the North American type strain VR-2332 and less than 60% homology with the European type strain LV. The obtained PRRSV clinical isolate was genetically close to the strains of JXA1, HEB1 and HUB2 which were dominantly prevalent in China in recent 3 years. The analysis of the hydrophilicity of GP3 protein of the PRRSV isolate showed that its first 57 amino acids were hydrophobic signal peptide sequences. The analysis results of antigenic epitope prediction of GP3 protein of the PRRSV isolate were basically the same as those of some other domestic and foreign PRRSV strains, indicating that the GP3 protein of the PRRSV isolate in this study had similar antigenic properties to that of other strains.

Key words: porcine reproductive and respiratory syndrome virus, GP3 protein, cloning, sequence analysis