Abstract: N gene fragment was amplified from PRRSV of cell RNA by RT-PCR and expressed it by prokaryotic expression vector pET-28a(+). A recombinant plasmid pET-28a-N was constructed and identified by restriction endonuclease digestion, then transformed into the E.coli BL21(DE3) plysS. The PRRSV N gene was expressed as a recombinant fusion protein and detected by SDS-PAGE and Western blotting. N gene fragment of 372 bp was amplified by RT-PCR, the recombinant bacteria was induced with IPTG and the expression protein was analyzed by SDS-PAGE. The results showed that bacteria contained the positive plasmid was induced to express with 1 mmol/L IPTG and 4 hours. A unique band was detected with the molecular mass of approximately 18 ku by SDS-PAGE. By analysis of Western blotting, the expressed production was reactive with the positive swine serum of PRRSV. PRRSV N gene was amplified and recombinant prokaryotic expression plasmid was constructed successfully. This showed that the high efficient expression of N protein was obtained which system of prokaryotic and eukaryotic expression. Using target protein after purified as coating antigen，an indirect ELISA was developed for detecting the anti-N antibody in the PRRSV serum by exploring the concentration of coating antigen and dilution degree of serum. 

Key words: porcine reproductive and respiratory syndrome virus; nucleoprotein; prokaryotic expression