31 Baculovirus DNA Replication

Abstract

The Baculoviridae are a diverse family of viruses pathogenic for arthropods, particularly insects of the order Lepidoptera (Blissard and Rohrmann 1990). They are characterized by large, rod-shaped virions that contain double-stranded, supercoiled DNA genomes ranging in size from 88 kb to more than 160 kb, depending on the viral strain. The virions are enclosed in large proteinaceous structures known as occlusion bodies, which function to protect virions and allow them to remain viable for extended periods. Baculoviruses are divided into two genera on the basis of occlusion body morphology; the nuclear polyhedrosis viruses (NPVs) are characterized by many virions present in each polyhedron-shaped occlusion body, whereas the granulosis viruses (GVs) normally have a single virion in much smaller occlusion bodies. Baculoviruses have drawn widespread interest due to their remarkable ability to over-express heterologous genes under the control of the strong polyhedrin gene promoter (Smith et al. 1983; Pennock et al. 1984). They are also being investigated for incorporation into insect pest management programs as alternatives to chemical insecticides (Leisy and van Beek 1992).

The best-characterized baculovirus, the Autographa californica multi-nucleocapsid NPV (AcMNPV), has a genome of 134 kb and is estimated to contain 154 genes (Fig. 1) (Ayres et al. 1994). A distinctive feature of the AcMNPV genome is the presence of eight homologous regions (hrs) composed of multiple repeated sequences that are dispersed throughout the genome (Cochran and Faulkner 1983; Guarino et al. 1986; Guarino and Summers 1986b; Ayres et al. 1994). hrs, which are prominently featured in this...