Baculoviridae

VIRION

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Envelopped. extracellular baculovirus virions can be found in two forms: OV (occluded virus) and BV (budded virus). The nucleocapsid is about 21 nm x 260 nm.

GENOME

Circular dsDNA, 80-180 kb in length, encoding for 100 to 180 proteins.

GENE EXPRESSION

REPLICATION

NUCLEUS

  1. Attachement of the viral glycoproteins to host receptors mediates endocytosis of the virus into the host cell.
  2. Fusion with the plasma membrane.
  3. The DNA genome is released into the host nucleus.
  4. Immediate early phase: host RNA polymerase transcribes viral genes involved in the regulation of the replication cascade, prevention of host responses and viral DNA synthesis.
  5. Late phase: The virally encoded RNA polymerase expresses late genes.
  6. Replication of the genome by rolling circle in nuclear viral factories.
  7. Nucleocapsids are formed which can either bud out through the cellular membrane and disseminate the infection or be occluded for horizontal transmission.
  8. Occlusion phase: the virus becomes occluded in the protein polyhedrin and the polyhedral envelope (calyx) is produced. Lysis of the cell releases the occluded virus.

Host-virus interaction

Apoptosis modulation

Several viral proteins are dedicated to inhibit host apoptosis. Among them, IAP3 is a RING-finger E3 ubiquitin ligase that ubiquitinates and subsquently targets host pro-apoptotic factors. Baculovirus caspase inhibitors P49 and P35 block virus-induced apoptosis downstream of effector caspase DrICE activation.

Cell-cycle modulation

Some baculoviruses encode viral cyclins such as ODV-EC27 or BmNPV ORF120 that maintains the host cells at the G2/M phase while permitting the virus DNA replication .