Identification of a novel protein associated with envelope of occlusion-derived virus in Spodoptera litura multicapsid nucleopolyhedrovirus.

Spodoptera litura multicapsid nucleopolyhedrovirus (SpltMNPV) ORF137 (Splt137) is one of 29 unique SpltMNPV ORFs. Splt137 has the potential to code for a polypeptide of 231 amino acid residues with predicted molecular weight of 27.5 kDa. Computer-assisted analysis of the predicted amino acid sequences of Splt137 protein showed 1 N-glycosylation site and 11 phosphorylation sites. For identification of Spit137, antibody was prepared by immunization of rabbits with purified Splt137 protein produced in Escherichia coli. This antibody was used to analyse Splt137 protein using Western blot. A 36-kDa protein was found both in the infected cells and envelope fractions of occlusion-derived virus (ODV) but could not be detected in the budded virus (BV). Tunicamycin treatment of SpltMNPV infected cells suggested that the 36-kDa protein had undergone N-glycosylation. Our data suggested that Splt137 protein was a novel envelope protein of ODV and might exist as a more complex form of 79-kDa protein in intact ODV. Further, transcriptional analysis with RT-PCR and 5' RACE analysis suggested that Splt137 might perform functions early and late in infection.