Characterization of bro-b gene of Spodoptera litura multicapsid nucleopolyhedrovirus

Spodoptera litura multicapsid nucleopolyhedrovirus (SpltMNPV) ORF125 (designated as the bro-b gene) is a member of the unique multigene family called the baculovirus repeated ORFs (bro) family. Computer-assisted analysis revealed that BRO-B contains a conserved Bro-N domain in its N-terminus and a single-stranded DNA (ssDNA) binding motif in the middle region. In vitro the bro-b gene transcription was present at 12 h post-infection (p.i.) and remained detectable up to 96 h p.i. Western blot analysis of BRO-B expression with an antiserum made against 6xHis tagged BRO-B expressed in Escherichia coli showed that it was present from 12 h through 96 h p.i. in vitro. Structural localization revealed that BRO-B could be found in the nucleocapsid components of both occlusion-derived virus (ODV) and budded virus (BV). Immunofluorescence analysis indicated that BRO-B is located only in the nucleus of infected S. litura cells. Furthermore, Western blot analysis indicated that BRO-B was associated with nuclear structures. These results suggested that BRO-B might be a nuclear-associated protein.