Article Figures & Data
Figures
- FIG. 1.
Organization and expression of the MHV-A59 genome. The structural relationships of the MHV-A59 genome- and subgenome-length mRNAs are shown. The virus ORFs are depicted in teal (nsp1-nsp16 genes), blue (ns2, ns4a, ns4b, and ns5a genes), and green (S, M, E, N, and I structural protein genes). The ORFs are defined by the genomic sequence of MHV-A59 as published by Coley et al. (20). The open red box represents the common 59-leader sequence, and the barred circle represents the programmed (−1) frameshifting element. The translation products of the genome- and subgenome-length mRNAs are depicted, and the autoproteolytic processing of the ORF1a and ORF1a/ORF1b polyproteins into proteins nsp1 to nsp16 is shown. A number of confirmed and putative functional domains in the nsp proteins are also indicated. NeU, uridylate-specific endoribonuclease; PL1, papain-like protease 1; PL2, papain-like protease 2.
- FIG. 2.
Model for coronavirus replication-transcription. The ORF1 of genomic RNA (red) is translated to produce pp1a and pp1ab, which assemble into an RTC (teal oval) that recognizes cis-acting elements at the 5′ and 3′ ends of the genome. This RTC copies the genome either continuously into genome-length template or discontinuously into the various subgenome-length minus-strand templates. The minus strands (blue) are used as templates for genomic and subgenomic mRNA synthesis. Only genomes are used as templates for minus-strand synthesis, i.e., replication. The RTCs engaging in plus-strand synthesis age and release their minus-strand templates, which are then degraded specifically.
Tables
- TABLE 1.
Enzymatic activities and characteristics of coronavirus nsp protein domains
Activity Location and designation Protein family Architecture Comments References Papain-like proteinase One or two PLpro domains within nsp3 Deubiquitinating enzyme family Finger-palm-thumb Fingertips contain zinc-binding domain 5, 33, 56 ADP-ribose 1"-phosphatase ADRP (or X) domain within nsp3 Macro-HS2A-fold family Three-layered α/β/α Also found in other plus-strand RNA viruses 53, 58 3C-like cysteine proteinase nsp5 (3CLpro or main protease, Mpro) Two-β-barrel proteinase family Twelve antiparallel β-strands Extra, α-helical, carboxyl-terminal domain III 3, 4, 95 RNA-dependent RNA polymerase RdRp domain within nsp12 Viral RdRp family Finger-palm-thumb (predicted) RdRp motif VI signature GDD replaced with SDD 19, 87 5′-to-3′ helicase (associated, NTPase, and RNA 5′-triphosphatase activities) HEL domain within nsp13 Superfamily 1 helicase Modeled to Escherichia coli Rep helicase Adjacent to amino-proximal, binuclear, zinc-binding domain 9, 35, 36, 70 3′-to-5′ exonuclease ExoN domain within nsp14 DEDD superfamily Hexahelical bundle (predicted) Unable to cleave ribose 2′-O-methylated RNA substrates 45, 75 Uridylate-specific endoribonuclease NendoU domain within nsp15 XendoU family Wing-body-wing (butterfly fold) Active in hexameric form; RNA bound to internal cavity 10, 11, 31, 34, 56a, 88 S-adenosylmethionine-dependent 2′-O-methyltransferase nsp16 (MT) Rrmj methyltransferase family Methyltransferase fold (predicted) Activity yet to be determined 75, 86
