Increased productivity of the baculovirus expression vector system by combining enhancing factors

The baculovirus expression vector system uses the polyhedrin promoter for the expression of foreign proteins. To increase the polyhedrin promoter activity, vectors were constructed by combining two transcription enhancers and the vp39 promoter. The transcription enhancers included homologous region 5 (hr5) and burst sequences (BSs). Seven vectors were constructed using combinations of these transcription enhancers, and their expression levels were compared in Autographa californica multicapsid nuclepolyhedrovirus (AcMNPV) and Bombyx mori NPV (BmNPV) using enhanced green fluorescent protein (EGFP). Our results indicate that most of the constructs increased the expression level of EGFP using the polyhedrin promoter. In particular, the vp39 promoter and BSs were the most effective in BmNPV and AcMNPV, respectively. Synergistic effects of the enhancing factors were observed only in AcMNPV by the vp39 promoter and BSs. The hr5 negatively affected the expression level of EGFP using the polyhedrin promoter and other enhancers in both viruses. The enhancing effect obtained by combining the three factors was higher in BmNPV than in AcMNPV. This was the first study to perform a comparative evaluation of enhancing factors that affect the expression efficiency of foreign protein using the polyhedrin promoter in both AcMNPV and BmNPV.