The occlusion derived form of baculovirus is specially adapted for primary infection of the host midgut epithelium. As such, the virion must contain the proteins essential for host range determination and initiation of infection. Because knowledge of virion composition is a prerequisite for functional investigation, this study used a combination of techniques to identify the proteins present within or associated with the occlusion-derived virus (ODV) virion. Thirtyone proteins, including proteins known to be essential for viral DNA replication, were identified with confidence. An additional 13 proteins were identified by using one of the three techniques. A comparison of gene conservation among the ODV proteins encoded in the 16 sequenced baculoviridae genomes is presented. With knowledge of the composition of ODV, it is now possible to target proteins and study their role(s) during primary infection.A utographa californica nucleopolyhedrovirus (AcMNPV) is the type species for the family Baculoviridae and it was used in this study. AcMNPV is a double-stranded DNA virus (132 kbp) that undergoes a biphasic life cycle in its lepidopteron host. Progeny nucleocapsids have two fates: during the early phase of infection, Ϸ16% of the intracellular copies of viral DNA are targeted for maturation at the cell surface to produce budded virus (BV) (1). The remaining nucleocapsids mature within the nucleus and are incorporated within a viral occlusion (occlusionderived virus, ODV). After primary infection of the insect gut by ODV, BV is produced and released into the hemocoel, and secondary infection results in insect death with subsequent release of viral occlusions into the environment. Because ODV is the viral form responsible for primary infection, knowing virion composition is fundamental for functional investigation of virulence and host specificity. The goal of this study was to determine the protein composition of the ODV virion. Such knowledge should aid in the understanding of the biology of AcMNPV, including genetic manipulation of the family Baculoviridae to enhance their function as microbial pesticides (2). Additionally, studies on the mechanism of envelope protein trafficking to intranuclear membranes and ODV envelope would be aided by comprehensive knowledge of ODV envelope composition.ODV is amenable to proteomic approaches for protein identification. It is easily purified and contains a small number of proteins. Previous studies suggest ODV contains between 13 and 35 proteins, most of which are unknown (3-13). ODV is incorporated within a crystalline occlusion, and the increased density of the occlusion allows it to be easily purified from in vitro or in vivo sources. A major concern when releasing the ODV from the crystalline matrix is protein degradation caused by the presence of proteases, particularly an insect alkaline protease (14). To inhibit protease activity, the occlusions are treated with HgCl 2 or diisopropyl fluorophosphate (14). After protease inactivation, ODV is released from the occlusion an...

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Study of the biology of the occlusion-derived virus (ODV) of the baculovirus Autographa californica nucleopolyhedrovirus provides opportunities to reveal new discoveries into the mechanism of several cellular pathways. The synchronous pulse of multiple ODV envelope proteins that integrate into the endoplasmic reticulum (ER) and traffic to the nuclear membranes on their way to the ODV envelope provide a unique tool to study the mechanisms of integral membrane protein trafficking from the ER to the outer and inner nuclear membrane. Studies of the formation of virus-induced, intranuclear membrane microvesicles provide insight on mechanisms that alter fluidity and regulate budding of the inner nuclear membrane. Since ODV is specially adapted for primary infection of the insect gut, studies of the structure and function of ODV envelope proteins reveals insights on the mechanism of viral invasion of the gut and this knowledge is fundamental for the development of new strategies for insect control. This review focuses on recent advances in understanding the source of the ODV envelope and the molecular events that sort and traffic integral membrane proteins from the ER to the ODV envelope. The composition of ODV is reviewed, however it is worth noting that the function of many ODV proteins are currently unknown.