Transient expression assay in a baculovirus system using firefly luciferase gene as a reporter

Transient gene expression assays were developed to assess the function of the regulatory sequences of baculoviruses Bombyx mori nuclear polyhedrosis virus (BmNPV) and Autographa californica nuclear polyhedrosis virus (AcNPV) in insect cells of Bombyx mori and Spodoptera frugiperda, respectively. DNA sequences encoding luciferase (luc) of the firefly Photinus pyralis was successfully employed in the expression assay as a reporter gene. Recombinant plasmids were constructed containing the luc gene under control of baculovirus-specific or heterologous promoters. Cotransfection of Bombyx mori and Spodoptera frugiperda cells with recombinant plasmids carrying virus-specific promoter sequences and BmNPV and AcNPV DNA, respectively, gave rise to efficient synthesis of luciferase (Luc), while heterologous promoters induced a low level of luc expression. We found that flanking sequences of the AcNPV DNA in the transfer plasmid contained an unknown promoter conferring an efficient luc expression. The activity of this promoter was modulated by the polh promoter sequences. The assay allows one to conduct highly sensitive monitoring of the transient expression of foreign genes from the transfecting plasmids prior to construction of recombinant viruses.