Characterization of late gene expression factor LEF-10 from Bombyx mori nucleopolyhedrovirus

The LEF-10 expression factor from the Bombyx mori nuclear polyhedrosis virus (BmNPV) does not have significant homology with other late expression factors and is thought to be a transcriptional cofactor. To investigate the function of LEF-10, a Red recombination system was used to knock out the lef-10 gene from the BmNPV genome and a lef-10 gene knockout virus (ko-Bacmid) was constructed. The lef-10 gene was repaired back to the viral genome using a Bac-to-Bac system to create the repaired virus (re-Bacmid). When ko-Bacmid was transfected into BmN cells, the detected titer of progeny virus in the medium was zero, whereas the titer of the progeny re-Bacmid remained at a level similar to that of the wild type virus (wt-Bacmid). The viral DNA replication, transcription and expression of viral early, late and very late genes after ko-Bacmid transfection into BmN cells were evaluated. The quantitative polymerase chain reaction showed that the ko-Bacmid viral genome replication level remained low and that the ko-Bacmid viral gene transcription level was significantly lower than those of wt-Bacmid and re-Bacmid. No expression of the early gene lef-3 was detected. These results suggest that the lef-10 gene has significant effects on DNA replication of the viral genome and BmNPV gene transcription at each phase and deletion of the lef-10 gene affects the level of expression of the viral early gene directly.