The GBNV-(To) K NSs gene was cloned into pRSET-C vector and overexpressed, as described in the materials and methods section, in C43 (DE3) E.coli cells. rNSs was purified from the soluble fraction by Ni-NTA affinity chromatography and the purity of the protein was checked by SDS-PAGE analysis. A single band corresponding to the expected molecular mass of 52 kDa was observed in the eluted fractions ( Fig. 2A lane 1-3) . The yield of the purified protein was 7-10 mg from 500 ml culture. The molecular mass of rNSs was confirmed by mass spectrometric analysis. The molecular mass thus obtained was 51810 Da, which agreed with that predicted from the sequence of histidine-tagged rNSs (52 kDa).