The N Terminus of Autographa californica Multiple Nucleopolyhedrovirus DNA Polymerase Is Required for Efficient Viral DNA Replication and Virus and Occlusion Body Production.

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) DNA polymerase (DNApol) plays a crucial role in viral DNA synthesis, and the N terminus (residues 1 to 186) is highly conserved in the baculovirus DNApol family. However, the functional role of the N terminus of DNApol has not yet been characterized. Here we report a functional analysis of the AcMNPV DNApol N terminus. We truncated the DNApol N terminus to construct truncation mutants Bac-GFP-PolΔ64, Bac-GFP-PolΔ110, and Bac-GFP-PolΔ186, which lack 64, 110, and 186 N-terminal residues, respectively. Although the truncation mutants rescued viral DNA synthesis and infectious virus production, the level of DNA replication decreased, and Bac-GFP-PolΔ64, Bac-GFP-PolΔ110, and Bac-GFP-PolΔ186 showed 10-fold, 89-fold, and 891-fold reductions in infectious viral yield compared to that of the wild-type repair virus, respectively. Production of occlusion bodies was compromised for all truncation mutants. Further bioinformatic analysis showed that the first 64 amino acids (aa) at the extreme N terminus contains a conserved α(-helix)-β(-sheet)-β-β secondary-structure region, and further downstream sequence from aa 67 to 186 is comprised of four conserved sequence motifs. Multiple alanine point substitutions in the α-β-β-β structure region or the four sequence motifs in the N terminus impaired viral DNA replication and resulted in reduction of virus yield and occlusion body production. Together, our results suggested that the secondary structure and four conserved motifs within the N terminus of AcMNPV DNApol are important for viral DNA synthesis, infectious virus yield, and production of occlusion bodies.