Continuous foreign gene expression in transformed lepidopteran insect cells

Protocols for the isolation of recombinant baculoviruses and their use for foreign gene expression in insect cells have been described in detail in the preceding chapters (also see refs. 1 –5 ). Generally, this approach involves the replacement of viral DNA sequences encoding the polyhedrin protein with foreign DNA sequences encoding the protein of interest. The recombinant virus is plaque-isolated, and used to infect cultured insect cells or larvae. The protein of interest will be expressed during the very late phase of infection, when polyhedrin would normally be expressed by the wild-type virus. One major advantage of baculovirus expression vectors is that they can be used to produce exceedingly large amounts of a recombinant protein. This is due to the strength of the polyhedrin promoter, which can induce the synthesis of a very large pool of mRNA for translation into large amounts of protein. A second big advantage of the baculovirus expression system is that insect cells have most of the protein-processing capabilities of higher eukaryotic cells (reviewed in ref. 6 ). Thus, proteins produced in recombinant baculovirusinfected cells can undergo coand posttranslational processing, resulting in an end product that is very similar, if not identical, to the native protein.