Replication of baculovirus DNA.

The Baculoviridae is a diverse family of pathogens that are infectious for arthropods and are characterized by a complex replication cycle that culminates in the occlusion of virions in a crystalline protein matrix (Blissard & Rohrmann, 1990). Over 400 lepidopteran species serve as hosts for these viruses, with a single virus isolate usually restricted to one or a few related species. In addition, they have been reported from species of the orders Hymenoptera, Diptera, Siphonoptera and Trichoptera, as well as in several crustaceans (Adams & McClintock, 1991; Martignoni & Iwai, 1986). Baculoviruses are divided into two genera based on occlusion body morphology; the nuclear polyhedrosis viruses (NPVs) (Rohrmann, 1994), which are characterized by many virions present in each polyhedronshaped occlusion body, and the granulosis viruses (GVs) (Crook, 1994), which normally have smaller occlusion bodies each containing only a single virion, and have been reported to infect only the Lepidoptera. Occlusion bodies function to protect virions against proteolysis and environmental decay; occluded virions may remain viable for many years in the environment. A decade ago baculoviruses and their molecular biology became the focus of intense interest because of their remarkable ability to hyperexpress heterologous eukaryotic genes under the control of the strong polyhedrin promoter (Smith et al., 1983; Pennock et al., 1984). Because such proteins are processed in a manner similar to their native form, this system has become widely exploited for the expression of proteins for biomedical and pharmaceutical research. In addition,