Genome of Invertebrate Iridescent Virus Type 3 (Mosquito Iridescent Virus)

Abstract

Iridoviruses (IVs) are classified into five genera: Iridovirus and Chloriridovirus, whose members infect invertebrates, and Ranavirus, Lymphocystivirus, and Megalocytivirus, whose members infect vertebrates. Until now, Chloriridovirus was the only IV genus for which a representative and complete genomic sequence was not available. Here, we report the genome sequence and comparative analysis of a field isolate of Invertebrate iridescent virus type 3 (IIV-3), also known as mosquito iridescent virus, currently the sole member of the genus Chloriridovirus. Approximately 20% of the 190-kbp IIV-3 genome was repetitive DNA, with DNA repeats localized in 15 apparently noncoding regions. Of the 126 predicted IIV-3 genes, 27 had homologues in all currently sequenced IVs, suggesting a genetic core for the family Iridoviridae. Fifty-two IIV-3 genes, including those encoding DNA topoisomerase II, NAD-dependent DNA ligase, SF1 helicase, IAP, and BRO protein, are present in IIV-6 (Chilo iridescent virus, prototype species of the genus Iridovirus) but not in vertebrate IVs, likely reflecting distinct evolutionary histories for vertebrate and invertebrate IVs and potentially indicative of genes that function in aspects of virus-invertebrate host interactions. Thirty-three IIV-3 genes lack homologues in other IVs. Most of these encode proteins of unknown function but also encode IIV3-053L, a protein with similarity to DNA-dependent RNA polymerase subunit 7; IIV3-044L, a putative serine/threonine protein kinase; and IIV3-080R, a protein with similarity to poxvirus MutT-like proteins. The absence of genes present in other IVs, including IIV-6; the lack of obvious colinearity with any sequenced IV; the low levels of amino acid identity of predicted proteins to IV homologues; and phylogenetic analyses of conserved proteins indicate that IIV-3 is distantly related to other IV genera.

Genomic and Proteomic Analysis of Invertebrate Iridovirus Type 9

“…The genome orientation and gene designation were defined by the start codon of the IIV-9 orf001R ortholog of the first conserved iridovirus core gene in mosquito IIV-3 (orf004R [5]). Four short ORF (orf007, -088, -061, -139) that were represented by dual heavily overlapping ORF in opposite orientations could not be resolved as forward or reverse by bioinformatics analysis alone.…”

“…There are two putative NUDIX hydrolase proteins (075R and 152L), and these may play an important role in regulating nucleotides in the host cell. Delhon et al (5) postulated that the IIV-3 ortholog of 075R (IIV-3 080R) might act similarly to the vaccinia virus NUDIX ortholog (with a D10R mutation) and function as a repressor of transcription and translation. The reported presence Forty-four genes that could be postulated to have a role in DNA metabolism or DNA replication were identified.…”

“…There is a consistent lack of genome colinearity between IV except with very closely related isolates, although all IV sequenced to date possess a core cohort of 26 conserved genes (8). In contrast to the vertebrate IV, the only fully sequenced IIV are IIV-6 (Chilo iridovirus [CIV]) (20) and IIV-3 (mosquito chloriridovirus [MIV]) (5). IIV-6 is the type species of the Iridovirus genus, with a genome of 212 kbp and a GϩC content of 29%; however, phylogenetic studies show that IIV-6 belongs in a clade distant from that of most iridoviruses (Fig.…”

Rana grylio virus thymidine kinase gene: an early gene of iridovirus encoding for a cytoplasmic protein

“…Based on the Eighth Report of the International Committee on Taxonomy of Virus (ICTV), the family Iridoviridae has been subdivided into five genera: Iridovirus, Chloriridovirus, Ranavirus, Lymphocystisvirus, and Megalocytivirus [3]. To date, 12 genome sequences of iridoviruses including at least one from each genus have been completely sequenced and analysed [2,[4][5][6][7][8][9][10][11][12][13][14]. These analyses show that iridoviruses encode a number of cellular protein homologues that may be mostly involved in nucleic acid metabolism, such as ribonucleotide reductase (RR), thymidylate synthase (TS), deoxyuridine triphosphatase (DUT), and purine nucleoside phosphorylase (PNP) [15].…”

Cloning, expression and subcellular distribution of a Rana grylio virus late gene encoding ERV1 homologue

“…To date, the genomes of twelve iridoviruses, including FV3, have been completely sequenced [8,9], and 26 core genes have been predicted to exist in all iridoviruses [10]. One of these is a gene belonging to ERV1 (essential for respiration and viability) family.…”