Cloning with baculoviruses. (a) The construction of a typical vector used for protein expression in baculoviruses. The gene of interest is cloned into a small plasmid between two sites (att) recognized by a site-specific recombinase, then introduced into the baculovirus vector by site-specific recombination. This generates a circular DNA product that is used to infect the cells of an insect larva. The gene of interest is expressed during the infection cycle, downstream of a promoter that normally expresses a baculovirus coat protein at very high levels. (b) Left: an insect larva infected with a recombinant baculovirus vector expressing a protein that produces a red color. Right: an uninfected larva.