ICTV Virus Taxonomy Profile: Nodaviridae

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ICTV VIRUS TAXONOMY PROFILES Sahul Hameed et al., Journal of General Virology 2019;100:3–4 DOI 10.1099/jgv.0.001170 ICTV

A. S. Sahul Hameed,1,* A. S. Ninawe,2 T. Nakai,3 S. C. Chi,4 K. L. Johnson5 and ICTV Report Consortium

Abstract The family Nodaviridae includes two genera, Alphanodavirus and Betanodavirus. The family name derives from the Japanese village of Nodamura where Nodamura virus was first isolated from Culex tritaeniorhynchus mosquitoes. Virions are non- enveloped and spherical in shape with icosahedral symmetry (T=3) and diameters ranging from 25 to 33 nm. The genome consists of two molecules of single-stranded positive-sense RNA: RNA1 and RNA2. The virion capsid consists of 180 protein subunits arranged on a T=3 surface lattice. Alphanodaviruses infect insects, whereas betanodaviruses are pathogens of fish. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of the Nodaviridae, which is available at www.ictv.global/report/nodaviridae.

Table 1. Characteristics of the family Nodaviridae

Typical Striped jack nervous necrosis virus (RNA1: AB056571; RNA2: AB056572), species Striped jack nervous necrosis virus, genus member: Betanodavirus

Virion Non-enveloped spherical particles, 25–33 nm in diameter, with or without surface projections Genome Bi-partite single-stranded positive-sense RNA of 3.1 kb (RNA1) and 1.4 kb (RNA2) with 5¢-terminal caps but without poly(A) tails Replication Cytoplasmic within virus-induced invaginations on the outer mitochondrial membrane Translation From capped genomic and subgenomic RNAs Host range Natural hosts are insects (Alphanodavirus) or fish (Betanodavirus) Taxonomy Two genera, each including four or more species

VIRION RNA molecules are encapsidated in the same virus particle, and both are required for infectivity. Both molecules are Virions are non-enveloped, roughly spherical in shape, capped at their 5¢-ends and lack poly(A) tails at their 3¢- 25–33 nm in diameter and have icosahedral symmetry ends [2]. (T=3) (Table 1, Fig. 1) [1]. Electron microscopy of nega- tively stained betanodaviruses shows surface projections; these are not observed in alphanodaviruses. Virion buoyant REPLICATION À3 density in CsCl ranges from 1.30 to 1.36 g cm . Virions are Virus replication is cytoplasmic. Infected cells contain sin- stable to pH values ranging from 2 to 9 and are resistant to gle-stranded RNAs corresponding to RNA1 and RNA2, as heating at 56 C for 30 min. well as the subgenomic RNA3 (387 nucleotides), which derives from the 3¢-terminus of RNA1 and is not packaged GENOME into virions (Fig. 2). In addition to RNA-dependent RNA polymerase activity, protein A binds to and drives invagina- The genome of nodaviruses consists of two molecules of tion of the outer mitochondirial membrane to provide the positive-sense single-stranded RNA; RNA1 (3.1 kb) encod- compartment where RNA replication occurs. RNA3 enco- ing protein A, an RNA-dependent RNA polymerase of des either one or two proteins; protein B2 (11 kDa) is about 112 kDa (983–1014 amino acids), and RNA2 (1.4 kb) encoded by all nodaviruses in a reading frame overlapping encoding protein a, the capsid protein precursor. Both that of protein A, and is a suppressor of RNA interference.

Received 10 October 2018; Accepted 17 October 2018; Published 15 November 2018 Author affiliations: 1Aquatic Animal Health Laboratory, C. Abdul Hakeem College, Melvisharam 632509, Vellore Dt, TN, India; 2Advisor, Department of Biotechnology, Government of India, CGO Complex, New Delhi 110003, India; 3Graduate School, Hiroshima University, Japan; 4National Taiwan University, Taipei, Taiwan, ROC; 5Department of Biological Sciences, University of Texas at El Paso, Texas 79968, USA. *Correspondence: A. S. Sahul Hameed, [email protected] Keywords: Nodaviridae; ICTV Report; taxonomy.

001170 Downloaded from www.microbiologyresearch.org by This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. IP: 54.70.40.11 3 On: Mon, 07 Jan 2019 22:22:03 Sahul Hameed et al., Journal of General Virology 2019;100:3–4

Fig. 1. Flock House virus particles. (Left) Image reconstruction. (Centre) Schematic representation of a T=3 icosahedral lattice. A1, B1 and C1 indicate three different quasi-equivalent copies of the capsid protein. (Right) Cryo-electron micrograph; the bar represents 50 nm. (Courtesy of N. Olson and T. Baker.)

Some nodaviruses also express protein B1 (11 kDa), which species encode capsid proteins that differ at >20 % of nucle- corresponds to the C-terminal region of protein A and is of otide or >13 % of amino acid positions (Alphanodavirus) or unknown function. Maturation of non-infectious provirions >15 % of nucleotide and >12 % of amino acid positions involves the autocatalytic cleavage of protein a into proteins (Betanodavirus). There is limited sequence identity between b (39 kDa) and g (4 kDa). the capsid proteins of members of different genera, or with those of a number of unclassified nodaviruses isolated from PATHOGENICITY prawns, nematodes and insects. Alphanodavirus infection results in the stunting, paralysis RESOURCES and death of the insect host. The infection of fish by betanodaviruses such as striped jack nervous necrosis virus or red- Full ICTV Online (10th) Report: www.ictv.global/report/ spotted grouper nervous necrosis virus causes neural nodaviridae. necrosis, encephalopathy or retinopathy and is associated with behavioural abnormalities and high mortality, posing Funding information significant problems for marine aquaculture [3, 4]. Production of this summary, the online chapter and associated resources was funded by a grant from the Wellcome Trust (WT108418AIA). TAXONOMY Acknowledgements The members of the two genera in this family infect insects Members of the ICTV 10th Report Consortium are Elliot J. Lefkowitz, Andrew J. Davison, Stuart G. Siddell, Peter Simmonds, Sead Sabanad- (Alphanodavirus) [5] or fish (Betanodavirus) [6]. Different zovic, Donald B. Smith, Richard J. Orton and Nick J. Knowles. Conflicts of interest The authors declare that there are no conflicts of interest.

References 1. Johnson KL, Reddy V. Structural studies of noda and tetraviruses. In: Miller LK and Ball LA (editors). The Insect Viruses. New York: Ple- num; 1998. pp. 171–223. 2. Johnson KN, Johnson KL, Dasgupta R, Gratsch T, Ball LA. Compar- isons among the larger genome segments of six nodaviruses and their encoded RNA replicases. J Gen Virol 2001;82:1855–1866. 3. Iwamoto T, Mise K, Mori K, Arimoto M, Nakai T et al. Establishment of an infectious RNA transcription system for Striped jack nervous necrosis virus, the type species of the betanodaviruses. J Gen Virol 2001;82:2653–2662. 4. Munday BL, Kwang J, Moody N. Betanodavirus infections of teleost fish: a review. J Fish Dis 2002;25:127–142. 5. Ball LA, Johnson KL. Nodaviruses of Insects. In: Miller LK and Ball LA (editors). The Insect Viruses. New York: Plenum; 1998. pp. 225– Fig. 2. Flock House virus (Alphanodavirus) genome organization and 267. replication strategy. 6. Yong CY, Yeap SK, Omar AR, Tan WS. Advances in the study of nodavirus. PeerJ 2017;5:e3841.

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