Objective To clone and express nucleoprotein( NP) gene of swine influenza virus( SIV) and to identify NP protein with good antigenicity. Methods The NP gene of A / swine / Henan /2 /2008( H3N2) was amplified with PCR. After digested by EcoR I and Xho I,the PCR products were cloned into prokaryotic expression vector p ET32 a and transformed into Rosetta strain. The recombinant vector,named p ET32a-NP,was identified with PCR,EcoR I / Xho I digestion and DNA sequencing. After sopropyl-beta-D-thiogalactopyranos...