Gene Regulation in Prokaryotes

Types of Genes

• Constitutive Genes: Always active, often called housekeeping genes.
• Facilitated Genes: Assist and help processes when needed.

Control Mechanisms in Prokaryotes

• Goal: Efficient use of carbon and energy sources.
• Levels of Control:
  1. Transcriptional Level (DNA Level): Proteins interact with promoters to regulate transcription.
  2. Post-transcriptional Events: If a gene is already transcribed, translation can be shut down.
  3. Post-translational Modifications: Degradation or modification of proteins to inhibit function.

Transcriptional Control

• DNA Binding Proteins:
  • Function by interacting with DNA in a sequence-specific manner through molecular contacts, not specific base sequences.
  • Important Domains:
    • Zinc Finger
    • Leucine Zipper
    • Helix-Turn-Helix (emphasized for memorization)
  • Typically homodimeric: Two identical subunits; each polypeptide chain has a domain interacting with DNA sequences.

DNA Sequences and Binding

• Inverted Repeat Sequences:
  • Specialized sequences present in the major groove of DNA.
  • Described as palindromic sequences (e.g., "race car").
  • Inversion allows for binding of each polypeptide in the dimer with each DNA strand.

Importance of these Mechanisms

• Efficient regulation of transcription is crucial for cellular conservation of resources.
• Many proteins discussed are DNA binding proteins, emphasizing their role in gene regulation.