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The N Terminus of Autographa californica Multiple Nucleopolyhedrovirus DNA Polymerase Is Required for Efficient Viral DNA Replication and Virus and Occlusion Body Production
Guoqing Chen, Qing Yan, Yang Fang, Lijuan Wu, Peter J. Krell and Guozhong Feng*
Journal of Virologya  , 2018, 92(11):1-20.

Abstract

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.