Comparative Study of Virion Structure, Protein Composition and Genomic DNA of Three Ascovirus Isolates

Abstract

The virions of three ascoviruses isolated from the noctuids Heliothis zea, Spodoptera frugiperda and Trichoplusia ni were compared with respect to their size and structure, protein composition and the size and relatedness of their DNAs. The virions of the isolates from H. zea (HAV) and T. ni (TAV) were allantoid in shape (400x130 nm), enveloped and contained an inner particle which appeared to have an internal lipid bilayer surrounding the DNA core. The virions of the S. frugiperda isolate (SAV) were similar in structure and size, but were bacilliform in shape, and after formation, were often occluded in vesiculate occlusion bodies. In preparations of purified virions of each isolate, at least 12 polypeptides were detected that ranged in size from 10K to 200K and contained a major species of about 50K. The genome of SAV was about 140 kbp in size, whereas those of TAV and HAV were approximately 180 kbp. Analysis of DNA fragment patterns of the three isolates generated with BamHI, HindIII or XhoI, as well as DNA-DNA dot blot and Southern blot hybridization studies, demonstrated that HAV and TAV were closely related but not identical. The DNA from SAV, however, did not hybridize with the DNA from either of the other isolates. Thus the ascovirus isolates from T. ni and H. zea are considered variants of the same virus, whereas the isolate from S. frugiperda is a separate member of the ascovirus group.

Phylogenetic analysis and possible function of bro-like genes, a multigene family widespread among large double-stranded DNA viruses of invertebrates and bacteria

“…The ascoviruses used, SfAV1a and HvAV3c, were isolated initially from the noctuid hosts Spodoptera frugiperda and Heliothis virescens, respectively (Federici et al, 1990). DpAV4 was isolated from its wasp host, Diadromus pulchellus (family Ichneumonidae), and from pupae of its lepidopteran host, Acrolepiopsis assectella (Family Yponeumonidae; Bigot et al, 1997).…”

Particle and genomic characteristics of a new member of the Ascoviridae: Diadromus pulchellus ascovirus.

“…However, the DpAV virion may have a genomic superhelical structure that is not detected in our experiments if the DpAV genome was nicked during DNA purification. It has been suggested that the genomes of Heliotis virescens ascovirus (HAV), Trichoplusia ni ascovirus (TAV) and Spodoptera frugiperda ascovirus (SAV) are linear (Federici et al, 1990), but these ascoviral genomes were not studied by PFGE. The DpAV genome contains 6-8 interspersed repeated sequences of 494 bp.…”

Circular configuration of the genome of ascoviruses.

“…Inoculated host larvae were reared on an artificial diet. Seven days postinoculation, the haemolymph with vesicles was collected and virions in the vesicles were purified as described by Federici et al (1990). Viral DNA was purified by centrifugation in a CsCl-EthBr gradient for 15 h. Five RENs were used to catalyse cleavage of the viral genomic DNAs prior to agarose gel analysis ; all RENs used were known to yield fewer than 14 fragmentation products.…”