science

Nidovirales

Nidovirales is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Nidovirales rather than just read about it. In short: Nidovirales is an order of enveloped, positive-strand RNA viruses which infect vertebrates and invertebrates. Host organisms include mammals, birds, reptiles, amphibians, fish, arthropods, molluscs, and helminths.

Key takeaways

Nidovirales belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Nidovirales to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Nidovirales from memory before moving on to harder problems.

Reference excerpt

Nidovirales is an order of enveloped, positive-strand RNA viruses which infect vertebrates and invertebrates. Host organisms include mammals, birds, reptiles, amphibians, fish, arthropods, molluscs, and helminths. The order includes the families Coronaviridae, Arteriviridae, Roniviridae, Tobaniviridae, and Mesoniviridae. Member viruses have a viral envelope and a positive-sense, single-stranded RNA genome which is capped and polyadenylated. Nidoviruses are named for the Latin nidus, meaning nest, as all viruses in this order produce a 3' co-terminal nested set of subgenomic mRNAs during infection.

Virology

Structure

Nidoviruses have a viral envelope and a positive-sense, single-stranded RNA genome which is capped and polyadenylated. The group 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. Member 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.

Genome Nidoviruses can be distinguished from other RNA viruses by a constellation of seven 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-dependent 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-Cys dyad, and is related to the SARS coronavirus main proteinase (Mpro). 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. Many 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 or ADP-ribose 1''-phosphate phosphatase activities and cyclic nucleotide phosphodiesterase.

Phylogenetics

The order 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 encode both a 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. Nidoviruses as a group have the largest RNA genomes of viruses. The largest reported genomes for RNA viruses are Crassostrea gigas nidovirus (CGNV) and Pacific oyster nidoviirus 1 (PONV 1); they are biseqmented, ~64kb in size, and infect Pacific oysters. They are members of a widely distributed group of viruses that belong to the proposed family Megarnaviridae. Previously, the largest reported genome was the 41.1kb, nonsegmented genome of planarian secretory cell nidovirus (PSCNV) that infect a planarian flatworm.

Taxonomy The following suborders and families are recognized (-virineae denotes suborders and -viridae denotes families):

See also Animal viruses Coronaviruses Serpentoviruses

References

Ziebuhr, J; Snijder, EJ; Gorbalenya, AE (April 2000). "Virus-encoded proteinases and proteolytic processing in the Nidovirales". The Journal of General Virology. 81 (Pt 4): 853–79. doi:10.1099/0022-1317-81-4-853. PMID 10725411.

External links Nidovirales—ICTVdB—The Universal Virus Database, version 4. Nidovirales at the U.S. National Library of Medicine Medical Subject Headings (MeSH) NIH/MeSH "The Nidoviruses" ISBN 0306466341

Illustrations

Worked examples

Example 1 — a first encounter with Nidovirales

Start with the simplest possible case. Write down what Nidovirales claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Nidovirales before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Nidovirales ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Nidovirales

In research: Nidovirales appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Nidovirales in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Nidovirales is common in secondary-school and first-year university syllabi. It links to neighbouring topics Animal virology, Nidovirales, Riboviria, so understanding it makes those chapters shorter.
In everyday life: Look for Nidovirales outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Nidovirales in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Nidovirales means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Nidovirales out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Nidovirales in simple terms?

Why does Nidovirales matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Nidovirales?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Nidovirales.