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Gene Regulation in Bacteria

• Regulation of Transcription Initiation

  • Factors influencing transcription initiation include the presence of different regulatory proteins.

• The lac Operon

  • Regulated by catabolite activator protein (CAP) and lac repressor.
  • CAP responds to glucose levels to promote glucose utilization.

• The Tryptophan Operon

  • Comprises 5 structural genes for tryptophan synthesis.
  • Operon functions under negative transcriptional control by trp repressor, active when tryptophan is absent.

• Regulation of Transcription Elongation

  • Mechanisms such as attenuation and riboswitches regulate transcription continuation.

• Riboswitches

  • RNA elements that respond to metabolites, influencing transcription by folding changes.

• Regulation of Translation

  • Controlled by riboswitches and small RNAs (sRNAs) that modulate mRNA translation.

• Global Regulatory Systems

  • Regulatory networks that control multiple genes simultaneously.
  • Terms:
  • Regulon: A set of genes controlled by a common regulator.
  • Modulon: Operon networks under a global regulator, but individually controlled.

• Two-Component Systems

  • Comprise a sensor kinase and a response regulator to mediate environmental response.

• Second Messengers

  • Molecules like cAMP and ppGpp respond to signals and modify cellular processes.

• Catabolite Repression

  • Regulates preferential use of carbon sources during growth (diauxic growth).

• cAMP and CAP

  • CAP must bind cAMP to activate transcription of catabolite operons like lac.

• Quorum Sensing

  • Mechanism where bacteria sense cell density and regulate gene expression accordingly (e.g., light production in V. fischeri).