The Baculovirus Core Gene ac83 Is Required for Nucleocapsid Assembly and Per Os Infectivity of Autographa californica Nucleopolyhedrovirus

Abstract

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ac83 is a baculovirus core gene whose function in the AcMNPV life cycle is unknown. In the present study, an ac83-knockout AcMNPV (vAc83KO) was constructed to investigate the function of ac83 through homologous recombination in Escherichia coli. No budded virions were produced in vAc83KO-transfected Sf9 cells, although viral DNA replication was unaffected. Electron microscopy revealed that nucleocapsid assembly was aborted due to the ac83 deletion. Domain-mapping studies revealed that the expression of Ac83 amino acid residues 451 to 600 partially rescued the ability of AcMNPV to produce infectious budded virions. Bioassays indicated that deletion of the chitinbinding domain of Ac83 resulted in the failure of oral infection of Trichoplusia ni larvae by AcMNPV, but AcMNPV remained infectious following intrahemocoelic injection, suggesting that the domain is involved in the binding of occlusion-derived virions to the peritrophic membrane and/or to other chitin-containing insect tissues. It has been demonstrated that Ac83 is the only component with a chitin-binding domain in the per os infectivity factor complex on the occlusion-derived virion envelope. Interestingly, a functional inner nuclear membrane sorting motif, which may facilitate the localization of Ac83 to the envelopes of occlusion-derived virions, was identified by immunofluorescence analysis. Taken together, these results demonstrate that Ac83 plays an important role in nucleocapsid assembly and the establishment of oral infection.

Autographa californicaNucleopolyhedrovirus Ac76: a Dimeric Type II Integral Membrane Protein That Contains an Inner Nuclear Membrane-Sorting Motif

“…This protein also ought to be on the ODV surface to digest the chondroitin sulfate barrier of the peritrophic matrix of the host midgut, thus facilitating viral infection of epithelial cells (60). Ac83 is the only component with a chitin-binding domain in the PIF complex on the ODV envelope (46,62). Deletion of the chitin-binding domain of Ac83 results in the failure of AcMNPV oral infection of Trichoplusia ni larvae.…”

“…Deletion of the chitin-binding domain of Ac83 results in the failure of AcMNPV oral infection of Trichoplusia ni larvae. Therefore, Ac83 may be on the ODV surface and may be involved in ODV binding to the peritrophic membrane and/or other chitin-containing insect tissues (62). As the topology of integral membrane proteins is highly complex and easily influenced by a combination of factors, our illustration of the ODV integral envelope proteins is speculative and much work remains to be performed to determine the orientation of these proteins.…”

Autographa californica Multiple Nucleopolyhedrovirus AC83 is aPer OsInfectivity Factor (PIF) Protein Required for Occlusion-Derived Virus (ODV) and Budded Virus Nucleocapsid Assembly as well as Assembly of the PIF Complex in ODV Envelopes

“…The binding of ODVs to midgut epithelial cells appears to have a high degree of specificity and requires a number of viral proteins, which includes the per os infectivity factors (PIFs) that are all known to be membrane proteins located in the ODV envelope. To date, seven PIF proteins have been identified, PIF0 (ac138; P74), PIF1 (ac119), PIF2 (ac22), PIF3 (ac115), PIF4 (ac96), PIF5 (ac148; ODV-E56), PIF6 (ac68), and PIF7 (ac110) (6)(7)(8)(9)(10)(11)(12)(13)(14). Until recently, all PIF proteins were encoded by core genes, which are genes conserved in all baculovirus genomes sequenced to date.…”

“…Like PIF proteins, AC83 is encoded by a core gene, contains a transmembrane domain, and copurifies with the PIF complex (13,16). However, unlike pif genes, the deletion of ac83 results in the loss of nucleocapsid formation, and therefore no ODVs or BVs are produced (13,17).…”

“…Like PIF proteins, AC83 is encoded by a core gene, contains a transmembrane domain, and copurifies with the PIF complex (13,16). However, unlike pif genes, the deletion of ac83 results in the loss of nucleocapsid formation, and therefore no ODVs or BVs are produced (13,17). Similar results were observed after deletion of the homologous gene bm95 in Bombyx mori NPV (BmNPV) (17,18); however, deletion of specific AC83 domains can maintain BV production but oral infectivity is lost (13).…”