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.

Recently, researchers from China National Rice Research Institute of Chinese Academy of Agricultural Sciences (CAAS) report a functional analysis of the AcMNPV DNApol N terminus. Researchers truncated the DNApol N-terminus and constructed corresponding truncation mutants: Bac-GFP-PolΔ64, Bac-GFP-PolΔ110 and Bac-GFP-PolΔ186 that lack N-terminal 64, 110 and 186 residues, respectively. Although the truncation mutants rescued viral DNA synthesis and infectious viral 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 reduction in infectious viral yield compared to 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 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 αβββ 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. This study 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.

This study was supported by the National Natural Science Foundation of China (No. 31572006, 31701847), the Zhejiang Provincial Natural Science Foundation of China (No. LQ15C140004), the innovation project of the Chinese Academy of Agricultural Sciences and the Central Level Public Interest Research Institute for Basic R & D Special Fund Business (No. 2013RG001-2, 2014RG002-3). The research findings have been published online in Journal of Virology on March 21 (DOI: 10.1128/JVI.00398-18). More details are available on the link below: http://jvi.asm.org/content/early/2018/03/15/JVI.00398-18.full.pdf+html