Evaluation of a novel, short polyA signal from the Bombyx mori bidensovirus

Abstract

Bombyx mori bidensovirus (BmBDV) is the only virus which belongs to the new Bidnaviridae family established by the International Committee on Taxonomy of Viruses in 2012. The genes encoding the major capsid protein and DNA polymerase (pPolB) overlap partially at their 3′ untranslated regions, forming an extremely short, dual-function polyadenylation signal/stop codon (BmBDV polyA) to complete post-transcriptional modifications and terminate protein expression. Nevertheless, the functionality and usefulness of this signal regarding foreign genes remain unknown. To determine the effect of the BmBDV polyA on gene expression, the expression of the green fluorescent protein and firefly luciferase was evaluated with the BmBDV polyA, compared with the much larger SV40 polyA, under the control of the p5 or ie1 promoter. Fluorescence microscopy and dual luciferase assay both revealed enhanced expression of these proteins in the presence of the BmBDV polyA, meanwhile real-time qPCR also showed increased mRNA levels. Therefore, we conclude that the BmBDV polyA is a promising, characteristic polyA signal from an insect virus, and that it can promote gene expression at either the mRNA or protein levels. Additionally, this study also suggests that the BmBDV polyA potentially alleviates restrictions associated with the size of inserted fragments during constructing recombinant viruses.