The Autographa californica M Nucleopolyhedrovirus ac79 Gene Encodes an Early Gene Product with Structural Similarities to UvrC and Intron-Encoded Endonucleases That Is Required for Efficient Budded Virus Production

Molecular, Cellular, and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, Kansas, USA.
Journal of Virology (Impact Factor: 4.44). 03/2012; 86(10):5614-25. DOI: 10.1128/JVI.06252-11
Source: PubMed


The Autographa californica M nucleopolyhedrovirus (AcMNPV) orf79 (ac79) gene is a conserved gene in baculoviruses and shares homology with genes in ascoviruses, iridoviruses, and several bacteria.
Ac79 has a conserved motif and structural similarities to UvrC and intron-encoded endonucleases. Ac79 is produced at early
times during infection and concentrates in the nucleus of infected cells at late times, suggesting a cellular compartment-specific
function. To investigate its function, an ac79-knockout bacmid was generated through homologous recombination in Escherichia coli. Titration assays showed that budded virus (BV) production was reduced in the ac79-knockout virus compared to control viruses, following either virus infection or the transfection of bacmid DNA. The ac79-knockout virus-infected cells produced plaques smaller than those infected with control ac79-carrying viruses. No obvious differences were observed in viral DNA synthesis, viral protein accumulation, or the formation
of occlusion bodies in ac79-knockout and control viral DNA-transfected cells, indicating progression into the late and very late phases of viral infection.
However, comparative analyses of the amounts of BV genomic DNA and structural proteins in a given quantity of infectious virions
suggested that the ac79-knockout virus produced more noninfectious BV in infected cells than the control virus. The structure of the ac79-knockout BV determined by transmission electron microscopy appeared to be similar to that of the control virus, although
aberrant capsid protein-containing tubular structures were observed in the nuclei of ac79-knockout virus-infected cells. Tubular structures were not observed for ac79 viruses with mutations in conserved endonuclease residues. These results indicate that Ac79 is required for efficient BV

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