Complete genome sequence of invertebrate iridovirus IIV-25 isolated from a blackfly larva.

Members of the family Iridoviridae are animal viruses that infect only invertebrates and poikilothermic vertebrates. Invertebrate iridovirus 25 (IIV-25) was originally isolated from the larva of a blackfly (Simulium spp., order Diptera) found in the Ystwyth river near Aberystwyth, Wales. IIV-25 virions are icosahedral, have a diameter of ~130 nm, and contain a dsDNA genome of 204.8 kbp, with a G+C content of 30.32 %, that codes for 177 proteins. Here, we describe the complete genome sequence of this virus and its annotation. This is the fifth genome sequence of an invertebrate iridovirus reported.

Complete genome sequence of invertebrate iridovirus IIV30 isolated from the corn earworm, Helicoverpa zea.

Members of the family Iridoviridae are animal viruses that infect only invertebrates and poikilothermic vertebrates. The invertebrate iridovirus 30 (IIV30) was originally isolated from a larva of the corn earworm, Helicoverpa zea (order lepidoptera, Family Noctuidae) in western Australia. The IIV30 virions are icosahedral, have a diameter of about 130nm, and contain a dsDNA genome of 198.5kbp with 28.11% in GC content and 177 coding sequences. Here we describe its complete genome sequence and annotate the genes for which we could assign a putative function. This is the sixth genome sequence of an invertebrate iridovirus reported.

Complete genome sequence of invertebrate iridescent virus 22 isolated from a blackfly larva.

Members of the family Iridoviridae are animal viruses that infect only invertebrates and poikilothermic vertebrates. Invertebrate iridescent virus 22 (IIV-22) was originally isolated from the larva of a blackfly (Simulium sp., order Diptera) found in the Ystwyth river, near Aberystwyth, Wales, UK. IIV-22 virions are icosahedral, with a diameter of about 130 nm and contain a dsDNA genome that is 197.7 kb in length, has a G+C content of 28.05 mol% and contains 167 coding sequences. Here, we describe the complete genome sequence of this virus and its annotation. This is the fourth genome sequence of an invertebrate iridovirus to be reported.

P64, a novel major virion DNA-binding protein potentially involved in condensing the Spodoptera frugiperda Ascovirus 1a genome.

We recently identified 21 structural proteins in the virion of Spodoptera frugiperda ascovirus 1a (SfAV1a), a virus with a large, double-stranded DNA genome of 157 kbp, which attacks species of the lepidopteran family Noctuidae. The two most abundant virion proteins were the major capsid protein and a novel protein (P64) of 64 kDa that contained two distinct domains not known previously to occur together. The amino-terminal half of P64 (residues 1 to 263) contained four repeats (a recently recognized motif with an unknown function) of a virus-specific two-cysteine adaptor. Adjoined to this, the carboxy-terminal half of P64 (residues 279 to 455) contained 14 copies of a highly basic, tandemly repeated motif rich in arginine and serine, having an 11- to 13-amino-acid consensus sequence, SPSQRRSTS(V/K)(A/S)RR, yielding a predicted isoelectric point of 12.2 for this protein. In the present study, we demonstrate by Southwestern analysis that SfAV1a P64 was the only virion structural protein that bound DNA. Additional electrophoretic mobility shift assays showed that P64 bound SfAV1a as well as non-SfAV1a DNA. Furthermore, we show through immunogold labeling of ultrathin sections that P64 is a component of virogenic stroma and appears to be progressively incorporated into the SfAV1a DNA core during virion assembly. As no other virion structural protein bound DNA and no basic DNA-binding proteins of lower mass are encoded by the SfAV1a genome or were identified by proteomic analysis, our results suggest that P64's function is to condense the large genome of this virus and assist in packaging this genome into its virion.

Ascovirus P64 Homologs: A Novel Family of Large Cationic Proteins That Condense Viral Genomic DNA for Encapsidation.

Eukaryotic dsDNA viruses use small basic protamine-like proteins or histones, typically <15 kDa, to condense and encapsidate their genomic (g)DNAs during virogenesis. Ascoviruses are large dsDNA (~100⁻200 kbp) viruses that are pathogenic to lepidopteran larvae. Little is known about the molecular basis for condensation and encapsidation of their gDNAs. Previous proteomic analysis showed that Spodoptera frugiperda ascovirus (SfAV-1a) virions contain a large unique DNA-binding protein (P64; 64 kDa, pI = 12.2) with a novel architecture proposed to condense its gDNA. Here we used physical, biochemical, and transmission electron microscopy techniques to demonstrate that P64's basic C-terminal domain condenses SfAV-1a gDNA. Moreover, we demonstrate that only P64 homologs in other ascovirus virions are unique in stably binding DNA. As similar protein families or subfamilies were not identified in extensive database searches, our collective data suggest that ascovirus P64 homologs comprise a novel family of atypical large viral gDNA condensing proteins.