Baculovirus Diversity and Molecular Biology

Abstract

With the identification and characterization of a number of structural and nonstructural protein genes, advances have been made in our understanding of baculovirus structure, regulation of gene expression, and replication. Since less than 30% of the AcMNPV genome has been sequenced and characterized, the continued identification and assignment of function to baculovirus genes is perhaps the most crucial of enterprises now facing baculovirologists and is critical to the development of our understanding of the baculovirus genome and its replication. The size and diversity of baculovirus genomes appears to be strongly influenced by mobile DNA from the insect host. Also, transposon-mediated mutations of baculoviruses provide examples of functional inactivation of viral genes (FP phenotype mutations) and transcriptional activation (TE-D insertion). Another role transposable elements may play is the introduction of insect promoters and enhancers to the baculovirus genome. Since early baculovirus genes are likely transcribed in a way similar to normal insect genes, transposons that insert strong constitutive promoters or cellular enhancers near early baculovirus genes may cause mutations that are subsequently selected for. If this does occur, baculovirus early gene promoters may exhibit a great deal of variability in sequence and may resemble host promoters. Given the overall similarity between the genomes of OpMNPV and AcMNPV and the apparent absence of a region, similar to the AcMNPV HindIII-K/EcoR1-S in OpMNPV, it is intriguing to speculate that this region which contains two ORFs and the hr5 enhancer, may have been inserted into the AcMNPV genome by transposition, possibly delivering several helpful genes (35k and 94k) and a powerful enhancer. The highly repeated enhancer may have been subsequently amplified by recombination. In such a model, the acquisition of general or species-specific enhancers might influence both virulence and host range. Acquisition of general enhancers could increase the level of early gene expression, thus accelerating the cellular infection cycle and making the virus more virulent. Similarly, the acquisition of species-specific enhancers might affect host range by accelerating the infection cycle, but only in a specific host or cell type. One might therefore postulate that diversity in baculoviruses may reflect not only different selection pressures but also the diversity of mobile DNA within host insect species. Although our understanding of baculovirus diversity and molecular biology is rapidly advancing, many of the fundamental characteristics that define the unique nature of baculoviruses remain poorly understood. One fundamental feature of baculoviruses is the production of the two virion phenotypes, PDV and BV.(ABSTRACT TRUNCATED AT 400 WORDS)

N-terminal sequences from Autographa californica nuclear polyhedrosis virus envelope proteins ODV-E66 and ODV-E25 are sufficient to direct reporter proteins to the nuclear envelope, intranuclear microvesicles and the envelope of occlusion derived virus

“…ODV obtains its envelope from viral induced membranes within the nucleoplasm. The mature ODV is then occluded within a proteinaceous crystal matrix and upon lysis of the infected cells, occlusions are released into the environment to be consumed by another insect (2,3).…”

Characterization of the deoxyuridine triphosphatase gene of Ophiusa disjungens nucleopolyhedrovirus

“…Insect viruses, especially nPvs, which infect arthropods and consist of rod-shaped virions that contain large doublestranded, supercoiled DnA genomes ranging in size from 88 to 165 kilobase pairs (Blissard and rohrmann, 1990 ), are considered potential biocontrol agents of the larvae of many lepidoptera. nPvs typically produce two virion phenotypes of progeny virus: occlusion-derived virus and budded virus.…”

Untitled

“…GVs have been isolated exclusively from lepidopteran larvae [3][4][5]. On the other hand, although the vast majority of NPVs infect insects, a few infect crustaceans [6].…”