R1 plasmid

Key takeaways

R1 plasmid belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect R1 plasmid to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of R1 plasmid from memory before moving on to harder problems.

Reference excerpt

The R1 plasmid is a plasmid that was first isolated from Salmonella paratyphi bacteria in 1963. It is a short plasmid, composed of 97,566 nucleotides and 120 genes, that belongs to the IncFII plasmid group. There are about one to two copies of the R1 plasmid per chromosome. The R1 plasmid imparts multi-drug antibiotic resistance to its host bacteria. The "R" in "R1" stands for "resistance", and the R1 plasmid contains resistance factors, or R factors, giving it the power to resist certain antibiotics. It's known as a "low copy" plasmid, meaning that it exists in relatively few copies in any given bacteria. This characteristic allows the R1 plasmid to have an efficient plasmid stabilization system, that aids in stabilizing medium copy number plasmids. R1 must rely on a "Type II" segregation system. This plasmid system ensures that at least one copy is contained in each daughter cell after cell division.

Structure The R1 plasmid belongs to the IncFII plasmid group. The Inc plasmid group stands for incompatibility, and plasmids are classified into this group when two plasmids can't steadily propagate in the same host. The major incompatibility group involved in resistance and virulence gene transfer is the IncF group. Since R1 is an IncFII plasmid, that means it carries the FII replicon. This plasmid subtype often carries blaCTX-M genes.

Key genes and operons

There are 120 genes on the R1 plasmid, and these genes can be sorted into three different groups. The largest group, as seen in green in Figure 1, is the conjugative plasmid backbone. The region pictured in purple is primarily a Tn21-like transposon, and the smallest region pictured in yellow contains sequences resembling those of Klebsiella oxytoca.

Replication repA: Initiates replication at the origin of replication (oriV), which helps it control plasmid copy number. copA: regulates repA mRNA translation by using an antisense RNA, controlling the frequency of replication. copB: contributes to the control of copy numbers by acting as a repressor protein that inhibits RepA transcription. oriV: origin of replication. RepA is needed in order to initiate replication.

Partitioning ParM: this protein forms dynamic filaments that push plasmid copies to opposite poles of the cell ParR: recruits ParM to the plasmid by acting as a DNA-binding protein that recognizes the ParC centromere-like site. ParC: the centromere-like site where ParR binds.

Conjugation These genes enable horizontal gene transfer via conjugation, spreading the plasmid between bacteria.

TraI: relaxase that initiates transfer by nicking the plasmid at the origin of transfer (oriT) TraM, traJ, traY: regulatory proteins that control expression of the tra operon and assembly of the conjugative pilus. trb genes: encode structural proteins of the mating pair formation system, including pilus components. oriT: origin of transfer. This is where DNA processing begins for conjugation.

Antibiotic resistance genes The products of these genes provide multidrug resistance to commonly used antibiotics:

blaTEM-1: provides resistance to ampicillin by encoding β-lactamase. cat: chloramphenicol acetyltransferase gene, provides resistance to chloramphenicol. aadA: aminoglycoside adenyltransferase, provides resistance to streptomycin and spectinomycin. sul1: sulfonamide resistance.

Addiction system This genetic system stabilizes plasmid inheritance by killing plasmid-free segregants.

The Hok/sok system a post-segregational killing system of the plasmid, toxin-antitoxin system hok: encodes a toxin that kills cells without the plasmid. sok: short anti-sense RNA that inhibits hok mRNA translation in plasmid carrying cells.

Maintenance and stability These genes ensure plasmid molecules remain monomeric, aiding stable inheritance.

resD: plays a role in site-specific recombination, resolving plasmid multimers back to monomers at the cer site. ParM is a prokaryotic actin homologue which provides the force to drive copies of the R1 plasmid to opposite ends of rod shaped bacteria before division. CopA-like RNA, an antisense RNA involved in replication control of the plasmid.

Replication Replication of the R1 plasmid begins at the oriRI site on the plasmid. RepA is the plasma-encoded initiator protein that binds to oriRI in order to initiate replication. RepA needs a 188-bp region of DNA at minimum in order to bind. Initiation of the leading strand, primed by DnaG, occurs at a G-type priming signal. This signal is located 400 bp downstream of the RepA-binding sequences. A newly synthesized RepA protein is used by an oriR on the same template that it was synthesized on, a cis-specific action.

Partitioning system Ensures active segregation of plasmids during cell division, preventing plasmid loss. The R1 plasmid partitioning is a mechanism needed for the inheritance of the R1 plasmid. The par system is composed of the ParR and the ParC regions, that interact together. The par system determines the position of the replicon, ensuring that at the end of DNA Replication, the plasmid copies are well-positioned to start cell division. The par system also allows for the initiation of ParM formation. ParM produces two important cytoskeletal proteins, MreB, and actin. ParM is directed to move the plasmid copies to opposite cell poles. Cell division takes place, resulting in the partitioned plasmids in two daughter cells.

References

Illustrations

Worked examples

Example 1 — a first encounter with R1 plasmid

Start with the simplest possible case. Write down what R1 plasmid 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 R1 plasmid 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 R1 plasmid 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 R1 plasmid

In research: R1 plasmid 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 R1 plasmid 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: R1 plasmid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Plasmids, so understanding it makes those chapters shorter.
In everyday life: Look for R1 plasmid 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.

How to study R1 plasmid in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what R1 plasmid 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 R1 plasmid out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is R1 plasmid in simple terms?

The R1 plasmid is a plasmid that was first isolated from Salmonella paratyphi bacteria in 1963. It is a short plasmid, composed of 97,566 nucleotides and 120 genes, that belongs to the IncFII plasmid group.

Why does R1 plasmid 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 R1 plasmid?

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 R1 plasmid.