Baculovirus expression systems

Baculoviruses are insect-specific pathogens, producing occlusion bodies containing enveloped virus particles which spread infection between insects. These occlusions or polyhedra are composed mainly of a 30 KDa virus-encoded protein produced in the very late phase of virus replication. Polyhedrin protein is not required for virus replication in cell culture and so the gene coding region can be replaced with a foreign sequence of choice to generate a baculovirus expression vector. The inserted coding region is placed under the transcriptional control of the polyhedrin gene promoter by transfection of insect cells with circular or linear baculovirus DNA or via transposition in bacteria. The coding region can be modified to allow the addition of different secretion signal peptides or peptide tags or multiple gene promoters can be used for the expression of more than one protein. The baculovirus expression vector may also be modified by the removal of nonessential genes encoding products deleterious to recombinant protein production. High yields of protein are possible by scaling up insect cell cultures in serum-free medium. Despite their specificity for insect cells, baculoviruses can also be use to transduce human cells, where recombinant genes can be expressed if placed under the control of mammalian-specific gene promoters