Autographa californica M nucleopolyhedrovirus open reading frame 109 affects infectious budded virus production and nucleocapsid envelopment in the nucleus of cells

Autographa californica M nucleopolyhedrovirus (AcMNPV) open reading frame 109 (ac109) is conserved in all known baculovirus genomes, suggesting a crucial role in virus replication. Although viruses lacking ac109 have been previously characterized, the phenotypes differ from production of non-infectious virions to lack of virion production. To re-examine ac109 function, we constructed a recombinant AcMNPV bacmid, AcBAC109KO, with a deletion in ac109. We did not detect infectious budded virus after transfection of AcBAC109KO DNA into cells. In the nucleus, nucleocapsids had envelopment defects and polyhedra lacked virions. DNA synthesis and gene expression between AcBAC109KO and a control virus were similar. However, lower levels of non-infectious budded virus were detected from AcBAC109KO DNA-transfected cells compared to the parental virus using Q-PCR to detect viral DNA or by immunoblotting to detect a budded virus protein. Therefore, deletion of ac109 affects envelopment of nucleocapsids in the nucleus and the production of infectious budded virus.

► The AcMNPV ac109 gene is necessary for the production of infectious budded virus.
► ac109 mutants produce reduced levels of non-infectious budded virus.
► ac109 is required for the envelopment of nucleocapsids prior to occlusion.
► Viral DNA replication and gene expression are unaffected by the absence of ac109.