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''Nidovirales'' is an order of viruses with animal and human hosts (MERS-CoV and SARS-CoV). It includes the families ''Coronaviridae'', ''Arterivirus,'' ''Roniviridae'' and ''Mesoniviridae''. The order Nidovirales is named for the Latin ''nidus'', meaning nest, as all viruses in this order produce a 3' co-terminal nested set of subgenomic mRNA's during infection. ==Virology== This group consists of viruses which have positive-sense, single-stranded RNA genomes. As positive-sense genomes, the viruses can use some host cell proteins during replication and gene expression which occurs in the cytoplasm of the host cell. This group of viruses expresses structural proteins separately from the nonstructural 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 or inactivating specific proteins at the correct time in the virus life cycle, ensuring replication occurs at the right time. A large number of proteins have been identified on the genomes of ''Nidovirales'', but their 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''-phosphate phosphatase activities and cyclic nucleotide phosphodiesterase. Most, but not all, nidovirus subgenomic 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. The virus which has the largest known nonsegmented RNA genome of 31.5kb, the mouse hepatitis virus (MHV), is of the order nidovirales. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nidovirales」の詳細全文を読む スポンサード リンク
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