Replication of simian virus 40 origin-containing DNA during infection with a recombinant Autographa californica multiple nuclear polyhedrosis virus expressing large T antigen

Nucleocapsid Assembly of Baculoviruses

The baculovirus nucleocapsid is formed through a rod-like capsid encapsulating a genomic DNA molecule of 80~180 kbp. The viral capsid is a large oligomer composed of many copies of various protein subunits. The assembly of viral capsids is a complex oligomerization process. The timing of expression of nucleocapsid-related proteins, transport pathways, and their interactions can affect the assembly process of preformed capsids. In addition, the selection of viral DNA and the injection of the viral genome into empty capsids are the critical steps in nucleocapsid assembly. This paper reviews the replication and recombination of baculovirus DNA, expression and transport of capsid proteins, formation of preformed capsids, DNA encapsulation, and nucleocapsid formation. This review will provide a basis for further study of the nucleocapsid assembly mechanism of baculovirus.

Replication, integration, and packaging of plasmid DNA following cotransfection with baculovirus viral DNA

Infection-dependent replication assays have been used to identify numerous putative origins of baculovirus replication. However, plasmid DNA, when cotransfected into insect cells with Autographa californica multinucleocapsid nucleopolyhedrovirus (AcMNPV) DNA, replicates independently of any viral sequence in cis (11). Cotransfection of transfer plasmids and baculovirus DNA is a common procedure used in generating recombinant viruses and in measuring the level of gene expression in transient-expression assays. We have examined the fate of a series of vector plasmids in cotransfection experiments. The data reveal that these plasmids replicate following cotransfection and the replication of plasmid DNA is not due to acquisition of viral putative origin sequences. The conformation of plasmid DNA replicating in the cotransfected cells was analyzed and found to exist as high-molecular-weight concatemers. Ten to 25% of the replicated plasmid DNA was integrated into multiple locations on the viral genome and was present in progeny virions following serial passage. Sequence analysis of plasmid-viral DNA junction sites revealed no homologous or conserved sequences in the proximity of the integration sites, suggesting that nonhomologous recombination was involved during the integration process. These data suggest that while a rolling-circle mechanism could be used for baculovirus DNA replication, recombination may also be involved in this process. Plasmid integration may generate large deletions of the viral genome, suggesting that the process of DNA replication in baculovirus may be prone to generation of defective genomes.