Virulence Gene Regulation

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Questions and Answers

In bacterial transcriptional attenuation, what is the consequence of a ribosome stalling at a control codon within the leader sequence of mRNA?

  • Degradation of the mRNA transcript by recruiting RNases.
  • Premature termination of transcription due to formation of a terminator hairpin.
  • Continued transcription due to prevention of a terminator hairpin formation. (correct)
  • Increased translation of downstream genes by enhancing ribosome binding.

How do riboswitches like the T-box riboswitch regulate gene expression in response to tRNA charging?

  • By modifying tRNA structure to enhance or inhibit translation based on metabolite levels.
  • By altering mRNA secondary structure to either expose or sequester the ribosome binding site based on tRNA charging. (correct)
  • By directly binding to RNA polymerase and inhibiting transcription initiation when tRNA is uncharged.
  • By degrading mRNA transcripts when tRNA is charged, preventing unnecessary protein synthesis.

In Listeria monocytogenes, PrfA expression is controlled by an RNA thermosensor. What is the state of the Shine-Dalgarno sequence at low temperatures and how does this affect PrfA translation?

  • Sequestered within a hairpin structure; inhibiting PrfA translation. (correct)
  • Accessible; promoting PrfA translation.
  • Modified by methylation; either promoting or inhibiting PrfA translation depending on the specific modification.
  • Degraded by RNases; preventing PrfA translation.

Which of the following is the correct order of events in a typical two-component signal transduction system?

<p>Environmental stimulus detection → Sensor kinase autophosphorylation → Phosphotransfer → Response regulator phosphorylation. (C)</p> Signup and view all the answers

What is the primary function of quorum sensing in bacteria?

<p>To coordinate gene expression based on population density. (A)</p> Signup and view all the answers

Autoinducers are signaling molecules involved in quorum sensing. What is the relationship between bacterial population size and autoinducer concentration?

<p>Autoinducer concentration increases as population size increases. (D)</p> Signup and view all the answers

What is a key advantage of quorum sensing for pathogenic bacteria in the context of host infection?

<p>Delayed production of virulence factors until a sufficient bacterial population is established to overwhelm host defenses. (B)</p> Signup and view all the answers

Gram-negative bacteria utilize different types of autoinducers. Acyl-homoserine lactones (AI-1) are examples of which type of signaling molecule?

<p>Freely diffusible autoinducers that can passively cross cell membranes. (D)</p> Signup and view all the answers

Autoinducer-2 (AI-2) is considered a 'universal' quorum sensing signal in some bacterial species. What does 'universal' imply in this context?

<p>AI-2 is produced and recognized by a wide range of bacterial species, facilitating interspecies communication. (A)</p> Signup and view all the answers

In the LuxI/R system of quorum sensing, what is the role of LuxR?

<p>It is a receptor protein that binds AI-1 and activates gene transcription. (A)</p> Signup and view all the answers

Gram-positive bacteria often use peptide-based autoinducers. How do these autoinducers typically differ from those used by Gram-negative bacteria in terms of membrane permeability?

<p>Peptide autoinducers in Gram-positive bacteria are actively transported across the membrane, unlike the freely diffusible AI-1. (C)</p> Signup and view all the answers

In the AgrD/FsrD system of Gram-positive quorum sensing, what is the role of AgrB?

<p>It is responsible for processing and exporting the peptide autoinducer precursor (AgrD). (A)</p> Signup and view all the answers

What is the function of RNAIII in the Staphylococcus aureus Agr system?

<p>It is a regulatory RNA that affects the translation of target mRNAs, including virulence factors. (B)</p> Signup and view all the answers

In the context of the Staphylococcus aureus Agr system, what is the effect of Interfering AIP (AIP-I) on quorum sensing?

<p>AIP-I inhibits the quorum sensing response by competing with activating AIP for receptor binding. (C)</p> Signup and view all the answers

How does the AgrC protein in Staphylococcus aureus initiate signal transduction upon binding to an activating AIP?

<p>AgrC autophosphorylates and then phosphorylates the response regulator AgrA. (B)</p> Signup and view all the answers

What is the consequence of deleting the agr locus in Staphylococcus aureus on virulence factor production?

<p>Significantly reduced production of virulence factors controlled by quorum sensing. (C)</p> Signup and view all the answers

Consider a bacterial species that uses transcriptional attenuation for gene regulation. If there is a high concentration of the regulatory metabolite, what mRNA secondary structure is most likely to form in the leader region and what is the outcome on transcription?

<p>Terminator hairpin; transcription is terminated. (C)</p> Signup and view all the answers

For a thermosensor RNA regulator like in PrfA expression, what happens to the hairpin structure and RBS accessibility as temperature increases?

<p>Hairpin structure unfolds, RBS accessibility increases. (B)</p> Signup and view all the answers

In a two-component signal transduction system, what is the role of phosphotransfer from the sensor kinase to the response regulator?

<p>To modify the response regulator and alter its activity, typically in gene regulation. (B)</p> Signup and view all the answers

Which of the following is a characteristic difference between Gram-positive and Gram-negative quorum sensing systems in terms of autoinducer type?

<p>Gram-positive bacteria primarily use peptide autoinducers, while Gram-negative bacteria commonly use AHLs. (D)</p> Signup and view all the answers

Flashcards

Transcriptional Attenuation

Transcription and translation are coupled, influencing gene expression via ribosomes and riboswitches.

Riboswitches

Metabolite-sensing RNAs control the synthesis of the ligands they sense.

RNA Thermosensors

Hairpin structures in RNAs unfold as temperature rises, affecting translation.

Regulons

Independent genes controlled by the same regulatory protein.

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Small Regulatory RNAs (sRNAs)

Small RNAs regulate transcription and translation by base-pairing to mRNA

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Two-Component Signal Transduction

Systems converting environmental stimuli into a genetic response via phosphorylation.

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Quorum Sensing

Allows bacteria to determine population size and trigger specific gene expression.

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Autoinducers

Allow bacteria to determine relative population size, increasing with population.

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Advantages of Quorum Sensing

To delay virulence factors; colonize new areas when current region is overpopulated.

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Gram-Negative Autoinducers

Acyl-homoserine lactones that are freely diffusible.

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Gram-Positive Autoinducers

Signaling molecules primarily composed of amino acids; not freely traverse membranes.

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Study Notes

Transcriptional and Translational Coupling

  • Transcriptional and translational coupling attenuates transcription in bacteria gene regulation
  • This process involves ribosomes and riboswitches

Transcriptional Attenuation in Bacteria

  • Coupling of transcription, and translation in bacteria facilitates transcriptional attenuation

Riboswitches

  • Riboswitches are metabolite-sensing RNAs that typically control the synthesis of the ligand they sense
  • There are T-box riboswitches and Lys Riboswitches

Transcriptional Regulation via Regulons

  • Regulons are independent genes whose promoter is controlled by the same regulatory protein

Listeria Pathogenicity Island 1 (LPI-1)

  • LPI-1 includes genes such as plcA, prfA, hly, mpl, actA, plcB, orfX, and orfZ

PrfA Expression in Listeria

  • Environmental signals control its expression, especially via RNA thermosensors

Translational Regulation

  • RNA thermosensors regulate gene expression by forming hairpin structures that unfold as temperature increases
  • The Shine-Dalgarno (RBS) sequence is only accessible at high temperatures

Heat Shock Response

  • Heat shock response is governed by RpoH σ32

Small Regulatory RNAs (sRNAs)

  • Small RNAs regulate transcription and translation
  • They range from 50-500 nucleotides in length
  • Antisense RNA base-pairs to mRNA
  • Prevents translation in some instances and promotes translation in other instances.
  • sRNA is removed via endonuclease
  • RNase cleavage site in sRNA is protected by the chaperone Hfq

Two-Component Signal Transduction

  • Two-component signal transduction systems convert environmental stimuli to a genetic response

Quorum Sensing Definition

  • Quorum sensing allows cells to survey their environment for cells of their own kind
  • It involves the sharing of specific small molecules
  • Specific gene expression is triggered once a sufficient concentration of the signaling molecule is present

Bacterial Communication

  • Autoinducers allow bacteria to determine the relative population size
  • More autoinducers are produced as population size increases

Advantages of Quorum Sensing

  • Delays the production of virulence factors until the host is unable to respond
  • Allows colonization of new areas when the current region is overpopulated

Gram-Positive vs. Gram-Negative Bacteria

  • The signaling systems of gram-positive and gram-negative bacteria differ

Gram-Negative Autoinducers

  • Gram-negative bacteria utilize autoinducer I (AI-1) and autoinducer 2 (AI-2)
  • Autoinducers are freely diffusible

Gram-Negative Autoinducers Sensing

  • Gram-negative autoinducers are sensed by a sensor histidine kinase

LuxI/R System

  • The LuxI/R system (AI-1) involves an activator protein (LuxR) and a generator of the quorum signal (LuxI)

Gram-Positive Autoinducers

  • Composed primarily of amino acids
  • Amino acids autoinducers cannot freely traverse membranes

Gram-Positive Quorum Sensing

  • The Gram-positive quorum-sensing system involves peptide production and response
  • AgrB and FsrB are involved
  • GBAP signal transduction is mediated by AgrC/FsrC
  • AgrA/FsrA activate target genes
  • A peptide responder uses an RNPP protein to regulate target genes

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