Identification of an envelope protein (VP39) gene from shrimp white spot syndrome virus

White spot syndrome virus (WSSV) was purified from the tissues of experimentally infected crayfish (Procambarus clarkii) with high yield. Based on SDS-PAGE of purified WSSV and mass spectrometry analysis, a protein with the molecular mass of 39 kDa was identified to match an open reading frame (ORF), WSV339, of WSSV genome. This ORF was 849 bp in length, encoding a 283 amino acid polypeptide. The protein was named VP39 and its gene was termed as vp39. Temporal transcription analysis revealed that vp39 was a late gene. The gene was cloned into pET-GST vector and expressed as a fusion protein with glutathione S-transferase (GST) in Escherichia coli strain BL21 (DE3). Western blot analysis indicated that VP39 could be detected in the extracts of both the WSSV virions and the viral envelopes. It was further located in the WSSV virions as an envelope protein using immunoelectron microscopy.