File:Viruses-13-00435-g002-A.png

English: Genome organisation and gene expression of BToV. The subgenomic (sg) mRNA species are numbered from large to small, with the genome designated RNA1. BToV polyprotein processing of pp1a and pp1ab and the conserved domains of nonstructural proteins (nsps) are shown. U1 and U2 proteins may be translated from an unconventional CUG initiation codon. The internal (I) protein is encoded within the N gene in some beta-CoVs. The 5′-leader sequence present in the genome and sg mRNA 2 of ToV are indicated by a small red box, and terminator/promoter signals of ToV in sg mRNA3 to 5 by a small green box. Red and green arrows indicate the locations of transcription-regulating sequences (TRSs). Arrowheads indicate (deduced) cleavage sites by papain-like (orange) or 3C-like protease/main protease (red). Vertical dashed line shows a ribosomal frameshifting site. 3CLpro, 3C-like protease (main protease); EndoU, endoribonuclease; ExoN, exoribonuclease; HEL, helicase; Mac, macrodomains including ADP-ribose-1″phosphatase; NiRAN, nidovirus RdRp-associated nucleotidyltransferase; N-MT, guanosine N7-methyltransferase; O-MT, ribose 2′-O-methyltransferase; PDE, 2’, 5’-phosphodiesterase; PLpro, papain-like protease; RdRp, RNA-dependent RNA polymerase; TM, transmembrane domain; ZBD, zinc-binding domain.