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Signal recognition particle RNA

Signal recognition particle RNA is a physics 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 Signal recognition particle RNA rather than just read about it. In short: The signal recognition particle RNA, (also known as 7SL, 6S, ffs, or 4.5S RNA) is part of the signal recognition particle (SRP) ribonucleoprotein complex. SRP recognizes the signal peptide and binds to the ribosome, halting protein synthesis.

Signal recognition particle RNA — main illustration
Signal recognition particle RNA — illustration

Key takeaways

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

Reference excerpt

The signal recognition particle RNA, (also known as 7SL, 6S, ffs, or 4.5S RNA) is part of the signal recognition particle (SRP) ribonucleoprotein complex. SRP recognizes the signal peptide and binds to the ribosome, halting protein synthesis. SRP-receptor is a protein that is embedded in a membrane, and which contains a transmembrane pore. When the SRP-ribosome complex binds to SRP-receptor, SRP releases the ribosome and drifts away. The ribosome resumes protein synthesis, but now the protein is moving through the SRP-receptor transmembrane pore. In this way SRP directs the movement of proteins within the cell to bind with a transmembrane pore which allows the protein to cross the membrane to where it is needed. The RNA and protein components of this complex are highly conserved but do vary between the different kingdoms of life. The common SINE family Alu probably originated from a 7SL RNA gene after deletion of a central sequence. The eukaryotic SRP consists of a 300-nucleotide 7S RNA and six proteins: SRPs 72, 68, 54, 19, 14, and 9. Archaeal SRP consists of a 7S RNA and homologues of the eukaryotic SRP19 and SRP54 proteins. Eukaryotic and archaeal 7S RNAs have very similar secondary structures. In most bacteria, the SRP consists of an RNA molecule (4.5S) and the Ffh protein (a homologue of the eukaryotic SRP54 protein). Some Gram-positive bacteria (e.g. Bacillus subtilis) have a longer eukaryote-like SRP RNA that includes an Alu domain. In eukaryotes and archaea, eight helical elements fold into the Alu and S domains, separated by a long linker region. The Alu domain is thought to mediate the peptide chain elongation retardation function of the SRP. The universally conserved helix which interacts with the SRP54 M domain mediates signal sequence recognition. The SRP19-helix 6 complex is thought to be involved in SRP assembly and stabilises helix 8 for SRP54. binding Humans have three functional SRP RNA genes, conveniently named RN7SL1, RN7SL2, and RN7SL3. The human genome in particular is known to contain a large amount of SRP RNA related sequence, including Alu repeats.

Discovery SRP RNA was first detected in avian and murine oncogenic RNA (ocorna) virus particles. Subsequently, SRP RNA was found to be a stable component of uninfected HeLa cells where it associated with membrane and polysome fractions. In 1980, cell biologists purified from canine pancreas an 11S "signal recognition protein" (fortuitously also abbreviated "SRP") which promoted the translocation of secretory proteins across the membrane of the endoplasmic reticulum. It was then discovered that SRP contained an RNA component. Comparing the SRP RNA genes from different species revealed helix 8 of the SRP RNA to be highly conserved in all domains of life. The regions near the 5′- and 3′-ends of the mammalian SRP RNA are similar to the dominant Alu family of middle repetitive sequences of the human genome. It is now understood that Alu DNA originated from SRP RNA by excision of the central SRP RNA-specific (S) fragment, followed by reverse transcription and integration into multiple sites of the human chromosomes. SRP RNAs have been identified also in some organelles, for example in the plastid SRPs of many photosynthetic organisms, and in the nuclear ribosomal internal transcribed spacer region of several ectomycorrhizal fungi.

Transcription and processing Eukaryotic SRP RNAs are transcribed from DNA by RNA polymerase III (Pol III). RNA polymerase III also transcribes the genes for 5S ribosomal RNA, tRNA, 7SK RNA, and U6 spliceosomal RNA. The promoters of the human SRP RNA genes include elements located downstream of the transcriptional start site. Plant SRP RNA promoters contain an upstream stimulatory element (USE) and a TATA box. Yeast SRP RNA genes have a TATA box and additional intragenic promoter sequences (referred to as A- and B-blocks) which play a role in regulating transcription of the SRP gene by Pol III. In the bacteria, genes are organized in operons and transcribed by RNA polymerase. The 5′-end of the small (4.5S) SRP RNA of many bacteria is cleaved by RNase P. The ends of the Bacillus subtilis SRP RNA are processed by RNase III. So far, no SRP RNA introns have been observed.

Function

Co-translational translocation The SRP RNA is an integral part of the small and the large domain of the SRP. The function of the small domain is to delay protein translation until the ribosome-bound SRP has an opportunity to associate with the membrane-resident SRP receptor (SR). Within the large domain, the SRP RNA of the signal peptide-charged SRP promotes the hydrolysis of two guanosine triphosphate (GTP) molecules. This reaction releases the SRP from the SRP receptor and the ribosome, allowing translation to continue and the protein to enter the translocon. The protein transverses the membrane co-translationally (during translation) and enters into another cellular compartment or the extracellular space. In eukaryotes, the target is the membrane of the endoplasmic reticulum (ER). In Archaea, SRP delivers proteins to the plasma membrane. In the bacteria, SRP primarily incorporates proteins into the inner membrane.

Post-translational transport SRP participates also in the sorting of proteins after their synthesis has been completed (post-translational protein sorting). In eukaryotes, tail-anchored proteins possessing a hydrophobic insertion sequence at their C-terminus are delivered to the endoplasmic reticulum (ER) by the SRP. Similarly, the SRP assists post-translationally in the import of nuclear-encoded proteins to the thylakoid membrane of chloroplasts.

Structure

… excerpt ends here. Continue reading the full article.

Illustrations

Signal recognition particle RNA illustration
Signal recognition particle RNA illustration
Signal recognition particle RNA: Secondary structure of the human SRP RNA. Helices are numbered from 2 to 8. Helical sections in gray are named with lower case letters. Residues are numbered in increments of ten. The 5′- and 3′-ends are indicated. Highlighted are the two hinges and the small (Alu) and large (S, "specific") domain of the SRP RNA.
Secondary structure of the human SRP RNA. Helices are numbered from 2 to 8. Helical sections in gray are named with lower case letters. Residues are numbered in increments of ten. The 5′- and 3′-ends are indicated. Highlighted are the two hinges and the small (Alu) and large (S, "specific") domain of the SRP RNA.
Signal recognition particle RNA: The classical function of SRP in translation-translocation. A membrane separates the cytosol from the endoplasmic reticulum. A ribosome (light gray with A, P, and E sites) synthesizes a protein with a signal peptide (green) encoded by messenger RNA (indicated by a line with 5′- and 3′-ends). The elongated SRP (blue), with its large (LD) and small (SD) domains, forms a complex with the membrane-resident SRP receptor (SR). When SRP separates, the protein crosses the membrane through a channel or translocon. The signal peptide may be removed by signal peptide peptidase (SP) and the protein modified by oligosaccharyl transferase (OT).
The classical function of SRP in translation-translocation. A membrane separates the cytosol from the endoplasmic reticulum. A ribosome (light gray with A, P, and E sites) synthesizes a protein with a signal peptide (green) encoded by messenger RNA (indicated by a line with 5′- and 3′-ends). The elongated SRP (blue), with its large (LD) and small (SD) domains, forms a complex with the membrane-resident SRP receptor (SR). When SRP separates, the protein crosses the membrane through a channel or translocon. The signal peptide may be removed by signal peptide peptidase (SP) and the protein modified by oligosaccharyl transferase (OT).
Signal recognition particle RNA: SRP RNA features and nomenclature. The human SRP RNA secondary structure is outlined in light gray, and the 5′- and 3′-ends are indicated. Conserved motifs are shown in dark gray. Helices are numbered from 1 to 12, helical sections are designated by lower case letters, and helix insertions by dotted numbers. Tertiary interactions between the apical loops of helices 3 and 4, and between helices 6 and 8 are indicated dotted lines.
SRP RNA features and nomenclature. The human SRP RNA secondary structure is outlined in light gray, and the 5′- and 3′-ends are indicated. Conserved motifs are shown in dark gray. Helices are numbered from 1 to 12, helical sections are designated by lower case letters, and helix insertions by dotted numbers. Tertiary interactions between the apical loops of helices 3 and 4, and between helices 6 and 8 are indicated dotted lines.

Worked examples

Example 1 — a first encounter with Signal recognition particle RNA

Start with the simplest possible case. Write down what Signal recognition particle RNA claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 Signal recognition particle RNA 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 Signal recognition particle RNA 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 Signal recognition particle RNA

In research
Signal recognition particle RNA appears in physics 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 Signal recognition particle RNA 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
Signal recognition particle RNA is common in secondary-school and first-year university syllabi. It links to neighbouring topics Genes on human chromosome 14, Non-coding RNA, Protein biosynthesis, so understanding it makes those chapters shorter.
In everyday life
Look for Signal recognition particle RNA 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 Signal recognition particle RNA in 20 minutes

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

Frequently asked questions

What is Signal recognition particle RNA in simple terms?

The signal recognition particle RNA, (also known as 7SL, 6S, ffs, or 4.5S RNA) is part of the signal recognition particle (SRP) ribonucleoprotein complex. SRP recognizes the signal peptide and binds to the ribosome, halting protein synthesis.

Why does Signal recognition particle RNA matter?

Because it connects several physics 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 Signal recognition particle RNA?

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 Signal recognition particle RNA.

Tags

  • Genes on human chromosome 14
  • Non-coding RNA
  • Protein biosynthesis
  • RNA
  • Rfam pages needing a picture

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