Homologous region 3 from Bombyx mori nucleopolyhedrovirus enhancing the transcriptional activity of heat shock cognate 70-4 promoter from Bombyx mori and Bombyx mandarina in vitro and in vivo.

The heat shock cognate 70-4 protein gene promoter (HSC70-4p) from Bombyx mori (BmHSC70-4p) is an ideal candidate for the transgenic silkworm due to its high transcriptional activity, and the homologous region 3 from Bombyx mori nucleopolyhedrovirus (BmNPVhr3) functions as an enhancer for several promoters. Using luciferase as a reporter gene and transient expression system in vivo and in vitro, we found that BmNPVhr3 can significantly increase the transcriptional activity of BmHSC70-4p and HSC70-4p from Bombyx mandarina (BmandHSC70-4p). Moreover, the transcriptional activity of the combination of BmHSC70-4p and BmNPVhr3 changed with developmental stages and hormone titers. These results suggest that the combination of BmHSC70-4 promoter and BmNPVhr3 enhancer is more effective candidate for the transgene or stable cell expression system in Bombyx mori.