ICTV Virus Taxonomy Profile: Roniviridae

Abstract

The family Roniviridae includes the genus Okavirus for three species of viruses with enveloped, rod-shaped virions. The monopartite, positive-sense ssRNA genome (26-27 kb) contains five canonical long open reading frames (ORFs). ORF1a encodes polyprotein pp1a containing proteinase domains. ORF1b is expressed as a large polyprotein pp1ab by ribosomal frameshifting from ORF1a and encodes replication enzymes. ORF2 encodes the nucleoprotein. ORF3 encodes two envelope glycoproteins. ORFX encodes a putative double membrane-spanning protein. Roniviruses infect shrimp but only yellow head virus is highly pathogenic. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Roniviridae, which is available at ictv.global/report/roniviridae.

Keywords: ICTV Report; Okavirus; Roniviridae; shrimp; taxonomy.

Fig. 1.

(a) Negative-contrast electron micrograph of gill-associated virus. (b) Negative-contrast electron micrograph of a partially disrupted yellow head virus virion displaying the internal nucleocapsid. (c) Schematic illustration of a ronivirus virion. (d) Thin-section electron micrograph of unenveloped cytoplasmic nucleocapsids in gill-associated virus-infected shrimp cells. The bars represent 100 nm. Courtesy of K. M. Spann, P. Loh, J. A. Cowley and R. J. McCulloch; panels (a), (b) and (c) reproduced with permission from [2].

Fig. 2.

Yellow head virus genome (g RNA1, 26 662 nt) and the two 3′-coterminal sub-genomic RNAs, sg mRNA2 and sg mRNA3. ORF1a hydrophobic regions HD1–HD4 (yellow). Functional domains (pink) - ORF1a: 3C-like protease (3CLP) and papain-like protease domains PLP1 and PLPx; ORF1b: nidovirus RdRP-associated nucleotidyltransferase (NiRAN); RNA-directed RNA polymerase (RdRP); cysteine- and histidine-rich zinc-binding domain (ZBD); superfamily 1 helicase (Hel1); exoribonuclease (ExoN); guanosine N7-methyltransferase (N-MT); and ribose 2′-O-methyl transferase (O-MT). ORF2 encodes the nucleoprotein (p20). ORF3 encodes a precursor polyprotein (pp3), which undergoes post-translation processing to generate envelope glycoproteins (gp116 and gp64) and an N-terminal triple membrane-spanning fragment (p25). ORFX is an alternative reading frame in ORF3 encoding a small double membrane-spanning protein (px). RFS - ribosomal frameshift site upstream of the ORF1a stop codon that allows translation of pp1ab. Known (▼) and likely (∇) sites of proteolytic cleavage of pp1a and pp1ab; signal peptidase type 1 cleavage sites in pp3 (↓).