The development of baculovirus expression vectors

Abstract

The major attraction of baculoviruses as an expression vector system was originally the virus-encoded polyhedrin gene. This produces large amounts of polyhedrin protein (28–30 kDa) in virus-infected insect cells in the latter stages of the replication cycle (see Chapter 1). The protein is required in the course of a normal infection cycle to package virus particles within occlusion bodies or polyhedra, which protect the virus particles in the environment between susceptible hosts. Although polyhedra are required to infect insects per os, their production is not necessary to maintain an infection in cultured cells in vitro. The redundancy of the polyhedrin protein was demonstrated by making deletions in the coding sequence which did not affect the synthesis of infectious, non-occluded virus particles (ECV) in the late phase of the infection cycle, in cell culture (Smith et al., 1983a). It was then a logical step to replace the polyhedrin coding region with foreign gene sequences and thus derive recombinant protein from the polyhedrin promoter. Polyhedrin-negative viruses can be propagated in vivo by injecting ECV directly into the haemolymph (see Chapter 10).