title: 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.
abstract: 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 production.
authors.affiliation: Molecular, Cellular, and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, Kansas, USA.
authors.forename: Wenbi
authors.initials: W
authors.lastname: Wu
authors.forename: A Lorena
authors.initials: AL
authors.lastname: Passarelli
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004720:Endonucleases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D007438:Introns; D008969:Molecular Sequence Data; D017924:Nucleopolyhedroviruses / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000502:physiology*; D021381:Protein Transport; D016415:Sequence Alignment; D018411:Spodoptera; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D057074:Virus Release
chemical_list: D014764:Viral Proteins; D004720:Endonucleases