Chapter 9: Sensing and Responding to the Environment

Learning Objectives

  • Define signal transduction

  • Differentiate one and two-component systems

  • Identify sensor and response regulator in both systems

  • Describe use of reporter plasmids in studying regulatory systems

  • Interpret data from reporter plasmids and knock-out mutants

Signal Transduction

  • Prokaryotes sense environmental changes (chemical gradients, pH, etc.)

  • Responses vary over time scales: immediate behavior changes vs. gene expression alterations

One and Two-component Systems

One-component Systems

  • Composed of a single protein with two domains: sensor kinase and response regulator

  • Signal detection by binding environmental chemicals; triggers kinase activity leading to phosphorylation of response regulator

  • Activates gene expression in response to environmental changes

Two-component Systems

  • Comprised of two separate proteins: sensor (detects signal) and response regulator (interacts with DNA)

  • More efficient response, as the response regulator is free-floating in the cytoplasm

  • Commonly leads to faster responses than one-component systems

Responses in Regulatory Systems

  • Specific responses based on output domain functions

  • Three classes of output domains: enzymatic activity, protein binding, and DNA binding (majority)

Knock-out Mutants and Complements

Knock-out Mutants

  • Created by deleting a gene to study phenotypic effects (e.g., fliC gene in swimming motility)

Laboratory Plasmids

  • Two types: expression plasmids (produce proteins) and reporter plasmids (determine gene expression)

  • Reporter plasmids: contain a promoter linked to a reporter protein to measure expression

Complements and Polar Effects

  • Complement mutants by reintroducing the original gene via plasmids to assess gene function

  • Knock-out mutations denoted with Δ; complements with +.

  • Phenotype restoration confirms gene's essentiality

References

  • Jung, H. et al., PLoS Comput. Biol. (2020)

  • Mitrophanov, A. Y. & Groisman, E. A., Genes Dev. (2008)