ENTOMOPOXVIRUSES ASSOCIATED WITH GRASSHOPPERS AND LOCUSTS: BIOCHEMICAL CHARACTERIZATION

Abstract

AbstractEntomopoxviruses (EPVs) are large DNA viruses with structural similarities to vertebrate poxviruses. EPV virions are occluded in large (3–15 μm in diameter) proteinaceous occlusion bodies (OBs). To date, EPVs are reported from 15 species of grasshoppers and locusts. The current information on the biochemical characterization of these EPVs is summarized in our review. The DNA genomes of grasshopper and locust EPVs analysed to date have a G+C ratio of approximately 18.5% and genome size estimates generated by various methods range from 180 to 194 kilobase pairs (kbp). Restriction endonuclease enzyme analysis of a number of grasshopper and locust EPV DNAs shows the virus isolates to be distinct and the technique will be useful in identifying virus isolates. The structural proteins of certain grasshopper EPVs have also been analysed. Forty to 50 polypeptides ranging in molecular weight from 12 to 200 kilodaltons (kDa) have been detected by SDS-PAGE analysis of virions released from OBs and the polypeptide profiles are distinct for many of the virus isolates. The proteinaceous matrix of the OB of EPVs contains one predominant protein referred to as spheroidin. The spheroidin protein from most grasshopper EPVs is approximately the same molecular weight, 107 kDa, when analysed by SDS-PAGE. As with other groups of occluded insect viruses, grasshopper EPVs have a protease activity associated with OBs derived from infected insects. The possible role of this protease activity in the infection cycle is discussed. Finally, the role of various molecular techniques for the detection and identification of EPV infections in laboratory and field populations of grasshoppers and locusts is discussed. The development of EPV-specific monoclonal antibodies and DNA hybridization probes for the detection of virus infections is reviewed. As well, the possible use of polymerase chain reaction and randomly amplified polymorphic DNA fingerprinting techniques for the detection and identification of EPV infections is discussed.