English: Roniviridae. Schematic representation of the 26,662 nt polyadenylated (+) single-stranded RNA genome of yellow head virus (g RNA1) and the two 3′-coterminal sub-genomic RNAs, sg mRNA2 and sg mRNA3. Functional domains in ORF1a: hydrophobic regions (HD1–HD4, yellow boxes), 3C-like protease (3CLP), papain-like protease (PLP1) and a domain with homology to PLP1 but lacking the canonical α + β fold of papain-like proteases (PLPx). Functional domains in 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); N7-methyltransferase (N-MT); and 2′-O-methyl transferase (O-MT). ORF2 encodes the nucleoprotein (p20). ORF3 encodes a precursor polyprotein (pp3) which undergoes post-translational processing to generate envelope glycoproteins (gp116 and gp64) and an N-terminal triple-membrane-spanning fragment of unknown function (p25). ORFX is an alternative reading frame in ORF3 encoding a putative small double-membrane-spanning protein (px). The ribosomal frameshift site (RFS) mediates a programmed (-1) frameshift upstream of the ORF1a stop codon and thus allows translation to be continued into ORF1b to produce polyprotein pp1ab. Known (▼) and likely (∇) sites of proteolytic cleavage of expressed polyproteins pp1a and pp1ab are indicated together with the two signal peptidase type 1 cleavage sites in pp3 (↓).