The Bombyx mori nucleopolyhedrovirus (BmNPV)-based baculoviral expression vector system is among the most efficient expression vector systems for eukaryotic proteins especially when used in combination with silkworms as a host. We newly isolated a novel BmNPV strain (BmNPV H4) in Hokkaido, Japan that outperforms the type strain T3 in terms of both proliferation and expression of polyhedrin protein in silkworm larvae; however, it proliferates poorly in the BmN cell line.

We inferred the gene responsible for the differences in proliferation between viral strains by quantifying amino acid similarity distances in protein functional domains and identifying highly divergent alleles between the H4 and T3 strains. Among proteins that differ markedly in functional domain sequence between H4 and T3, we identified the F gene, which encodes the F protein, as a putative cause of proliferative differences between the two strains. Using recombinant viruses with the F protein-coding sequence exchanged between H4 and T3, we determined that the T3 F protein increases H4 proliferation in BmN while the H4 F protein does not improve T3 proliferation in silkworm larvae. Our results suggest that the BmNPV F protein can strongly affect viral proliferation in a genetic background-specific manner and may be an important target for manipulating the proliferation characteristics of BmNPV-based expression vectors.

基于家蚕核多角体病毒 (BmNPV) 的杆状病毒表达载体系统是最有效的真核蛋白表达载体系统之一，尤其是与作为宿主的家蚕结合使用时。我们在日本北海道新分离了一种新的 BmNPV 菌株 (BmNPV H4)，该菌株在蚕幼虫中多角体蛋白的增殖和表达方面均优于 T3 型菌株；然而，它在 BmN 细胞系中增殖不佳。

我们通过量化蛋白质功能域中的氨基酸相似性距离并鉴定 H4 和 T3 毒株之间高度不同的等位基因，推断出导致病毒毒株之间增殖差异的基因。在 H4 和 T3 之间功能域序列显着不同的蛋白质中，我们确定了F编码 F 蛋白的基因作为两个菌株之间增殖差异的推定原因。使用在 H4 和 T3 之间交换 F 蛋白编码序列的重组病毒，我们确定 T3 F 蛋白增加 BmN 中的 H4 增殖，而 H4 F 蛋白不改善家蚕幼虫中的 T3 增殖。我们的研究结果表明，BmNPV F 蛋白可以以遗传背景特异性方式强烈影响病毒增殖，并且可能是操纵基于 BmNPV 的表达载体增殖特性的重要目标。