The polydnavirus Campolekis sonorensis virus (CsV) is present in the oviducts of all adult C. sonorensis female wasps and appears to be required for these wasps to parasitize hosts successfully. Physical mapping, Southern blot analysis, and nucleotide sequence analysis demonstrate that the viral DNA B-specific sequences in cloned wasp DNA are colinear with viral genomic segment DNA B from nucleocapsids and are covalently linked to nonviral wasp sequences. Integrated DNA B terminates in 59-nucleotide imperfect direct repeats, but a single repeat exists in the extrachromosomal superhelical viral DNA B. Sequences near each junction form imperfect inverted repeats with sequences near the ends of an internal viral 540-base-pair repeat element gene. CsV appears to be the frst documented integrated, nonretroviral DNA virus of insects and probably is vertically transmitted as a provirus.

Baculoviruses are currently used as vectors for the transient high-level expression of foreign gene products in insect cells. In this study, we demonstrate that baculoviruses can also be made to continuously express a foreign gene product by using the promoter from IE1, an immediate early viral gene, to produce stably-transformed insect cells. This approach gave levels of foreign gene expression lower than those usually obtained with the lytic baculovirus expression vector system. Expression, however, was continuous and stable, and a complex human glycoprotein (tissue plasminogen activator) was processed more efficiently. We conclude that stable transformation is a feasible approach for baculovirus-mediated foreign gene expression in lepidopteran cells, particularly for products that are relatively poorly-expressed and/or processed in lytically infected cells.

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