Cloning and Expression in E．coli of Nucleocapsid Protein Gene of Porcine reproductive and respiratory syndrome virus

The nucleocapsid protein gene(orf 7)of Porcine reproductive and respiratory syndrome virus(PRRSV)was isolated from PRRSV genome by RT PCR．The gene was cloned into pMD 1 8一T vector,the recombinant plasmid pMD1 8N containing orf 7 was sequenced and compared with other PRRSV isolates．The result shown that the homologies between the cloned orf 7 and America type PRRSV ATCC VR一2332 reached 100％，the orf 7 was highly conservative sequence in PRRSV genome． The orf 7 was subcloned into prokaryofic expressing vector pGEX—KG，the recombinant plasmid named pGEX—KGN was constructed．The pGEX—KGN was used to tran sfo rnl into E colf BL21．Th e results of SDS—PAGE an d W estem—blot indicated that the nucleocapsid protein gene cloned in downstream of Glutathione S—tran sferase(GST)was expressed in a high level an d the recombinan t fusion protein， which was about 41kDa．had immunologicaily reactive activity．This study lay on foundation for th e development of the diagnosis meth ods in serology fo r PRRSV