Nidovirales
Encyclopedia
The Nidovirales are an order of virus
es with animal
hosts. It includes the families Coronaviridae
, Arterivirus
and Roniviridae
.
genome; this is the mouse hepatitis virus (MHV) which has a genome of 31.5kb. These genomes share the structure of eukaryotic mRNA and so the viruses can use some host cell proteins during replication and gene expression which occurs in the cytoplasm of the host cell. Unlike many viruses they do not have any polymerase in the virus particle as the genome can be read directly as mRNA when it first enters the host cell.
This group of viruses express the structural proteins separately from the non-structural ones. The structural proteins are encoded at the 3’ region of the genome
and are expressed from a set of subgenomic mRNAs. These viruses encode one main proteinase and between one and three accessory proteinases which are mainly involved in expressing the replicase gene. These proteinases are also responsible for activating/inactivating specific proteins at the correct time in the virus life cycle and so ensure replication occurs at the right time. There are still a large number of proteins which have been identified on the genomes of nidovirales but whose function has not yet been determined.
Other enzymes that may be present in the genome include papain-like proteases, ADP-ribose/poly(ADP-ribose)-binding and/or ADP-ribose 1"-phosphatase activities and cyclic nucleotide phosphodiesterase.
Most, but not all, nidovirus sub genomic RNAs contain a 5′ leader sequence derived from the 5′ end of the genomic RNA.
The frameshift that generates ORF1b frameshift occurs at a UUUAAAC heptanucleotide 'slippery' sequence located upstream of the ORF1a stop codon and a putative RNA pseudoknot structure.
dyad.
The Nidovirales can be divided into two clades depending on the size of the genome: those with large genomes (26.3-31.7 kilobases) which included the Coronaviridae and Roniviridae (the large nidoviruses) and those with small genomes (the small nidoviruses) - a clade that includes the distantly related Arteriviridae (12.7-15.7 kb). The large nidoviruses large nidoviruses encode both an 2'-O-methyltransferase
and a 3'-5' exoribonuclease
(ExoN) - the latter being very unusual for an RNA virus. They also encode a superfamily 1 helicase
, uridylate-specific endonuclease (an enzyme unique to Nidoviruses) and several proteases.
A virus belonging to this group - Cavally virus - has been isolated from mosquito
es. It appears to be unrelated to the other member of this order and probably is the first member of a new family.
Another virus has been isolated from mosquitoes - Nam Dinh virus - that appears to belong a new family in this order.
Another virus - White bream virus - isolated from fish may also belong to this order.
Gill-associated virus and Yellow head virus, both isolated from prawn
s, are members of this order.
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es with animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
hosts. It includes the families Coronaviridae
Coronaviridae
Coronaviruses are enveloped, single-stranded, positive-sense RNA viruses with club-shaped surface about 120-160 nm in diameter that resemble a “corona”.-Virology:...
, Arterivirus
Arterivirus
Arterivirus is a genus of virus, with type species equine arteritis virus. In 1996, the family Arteriviridae was included within the order Nidovirales. Arteriviruses are small, enveloped, animal viruses with an icosahedral core containing a positive-sense RNA genome...
and Roniviridae
Roniviridae
Roniviridae is a family of virus of the order Nidovirales. The name is derived from their rod like shape - rod like nidoviridae.-Virology:...
.
Virology
This group consists of viruses which have (+) sense single stranded RNA genomes. It contains the virus which has the largest known non segmented RNARNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
genome; this is the mouse hepatitis virus (MHV) which has a genome of 31.5kb. These genomes share the structure of eukaryotic mRNA and so the viruses can use some host cell proteins during replication and gene expression which occurs in the cytoplasm of the host cell. Unlike many viruses they do not have any polymerase in the virus particle as the genome can be read directly as mRNA when it first enters the host cell.
This group of viruses express the structural proteins separately from the non-structural ones. The structural proteins are encoded at the 3’ region of the genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
and are expressed from a set of subgenomic mRNAs. These viruses encode one main proteinase and between one and three accessory proteinases which are mainly involved in expressing the replicase gene. These proteinases are also responsible for activating/inactivating specific proteins at the correct time in the virus life cycle and so ensure replication occurs at the right time. There are still a large number of proteins which have been identified on the genomes of nidovirales but whose function has not yet been determined.
Other enzymes that may be present in the genome include papain-like proteases, ADP-ribose/poly(ADP-ribose)-binding and/or ADP-ribose 1"-phosphatase activities and cyclic nucleotide phosphodiesterase.
Most, but not all, nidovirus sub genomic RNAs contain a 5′ leader sequence derived from the 5′ end of the genomic RNA.
The frameshift that generates ORF1b frameshift occurs at a UUUAAAC heptanucleotide 'slippery' sequence located upstream of the ORF1a stop codon and a putative RNA pseudoknot structure.
Taxonomy
This order of viruses can be distinguished from other RNA viruses by a constellation of 7 conserved domains - 5'-TM2-3CLpro-TM3-RdRp-Zm-HEL1-NendoU-3' - with the first three being encoded in ORF1a and the remaining four in ORF1b. TM2 and TM3 and transmembrane domains; RdRp is the RNA polymerase; Zm is a Zn-cluster binding domain fused with a helicase (HEL1); 3CLpro is a 3C-like protease; and NendoU is an uridylate-specific endonuclease. The 3CLpro has a catalytic His-CysCysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
dyad.
The Nidovirales can be divided into two clades depending on the size of the genome: those with large genomes (26.3-31.7 kilobases) which included the Coronaviridae and Roniviridae (the large nidoviruses) and those with small genomes (the small nidoviruses) - a clade that includes the distantly related Arteriviridae (12.7-15.7 kb). The large nidoviruses large nidoviruses encode both an 2'-O-methyltransferase
Methyltransferase
A methyltransferase is a type of transferase enzyme that transfers a methyl group from a donor to an acceptor.Methylation often occurs on nucleic bases in DNA or amino acids in protein structures...
and a 3'-5' exoribonuclease
Exoribonuclease
An exoribonuclease is an exonuclease ribonuclease, which are enzymes that degrade RNA by removing terminal nucleotides from either the 5' end or the 3' end of the RNA molecule...
(ExoN) - the latter being very unusual for an RNA virus. They also encode a superfamily 1 helicase
Helicase
Helicases are a class of enzymes vital to all living organisms. They are motor proteins that move directionally along a nucleic acid phosphodiester backbone, separating two annealed nucleic acid strands using energy derived from ATP hydrolysis.-Function:Many cellular processes Helicases are a...
, uridylate-specific endonuclease (an enzyme unique to Nidoviruses) and several proteases.
A virus belonging to this group - Cavally virus - has been isolated from mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
es. It appears to be unrelated to the other member of this order and probably is the first member of a new family.
Another virus has been isolated from mosquitoes - Nam Dinh virus - that appears to belong a new family in this order.
Another virus - White bream virus - isolated from fish may also belong to this order.
Gill-associated virus and Yellow head virus, both isolated from prawn
Prawn
Prawns are decapod crustaceans of the sub-order Dendrobranchiata. There are 540 extant species, in seven families, and a fossil record extending back to the Devonian...
s, are members of this order.
External links
- Nidovirales - ICTVdB - The Universal Virus Database, version 4.
- NIH/MeSH
- "The Nidoviruses" at Amazon.com