The Autographa californica multiple nucleopolyhedrovirus Ac132 plays a role in nuclear entry

A recent study found that the Autographa californica multiple nucleopolyhedrovirus (AcMNPV) Ac132 is a nucleocapsid-associated protein and required for budded virion (BV) production. We therefore initiated experiments aimed at understanding how Ac132 is involved in AcMNPV infection. An 80 bp region of ac132 was replaced with a chloramphenicol resistance gene to construct vAc132KO. Transfection of vAc132KO into Sf9 cells resulted in a single-cell infection phenotype, consistent with findings reported in a previous study. Interestingly, BVs were observable in the supernatants, and the BV production in the supernatant was comparable with that present in supernatants from a WT control. These results suggest that the ac132 deletion does not affect the egress of nucleocapsids from the transfected cells to form BVs, but the BVs are non-infectious. Transfection with DNA extracted from vAc132KO BVs could establish infection in Sf9 cells, indicating that the deletion does not affect the integrity of the viral genomic DNA in non-infectious progeny BVs. To monitor the traffic of nucleocapsids without Ac132, two mCherry proteins were fused with the major capsid protein VP39 to construct vAc132KO : 2mC. Using confocal microscopy, we observed that the nucleocapsids of vAc132KO : 2mC could not enter the nucleus and instead remained docked at the nuclear membrane. This study provides a new understanding of the nuclear entry of baculoviruses.