Lecture Notes: Positive Control in Transcription

Overview

• Positive control involves activator proteins that facilitate transcription.
• Activator proteins help RNA polymerase bind more efficiently to the promoter.

Activator Binding Sites

• Proximity to Promoter:
  • Close proximity: Direct assistance in promoter recognition.
  • Distant binding sites: DNA looping promotes necessary contacts for transcription.

Function of Activator Proteins

• Need specific conditions or molecules to bind to the DNA.
• Example: Maltose Operon in E. coli
  • Regulates enzymes for maltose catabolism.
  • Activator Protein: MALT (specific for the Maltose operon).

Transcription Regulation

• Absence of Maltose:
  • MALT cannot bind to the activator site due to incorrect shape.
  • RNA polymerase binds weakly or not at all, halting transcription.
• Presence of Maltose:
  • Acts as an effector or inducer molecule.
  • Binds to MALT, changing its conformation.
  • MALT can now bind to the activator site.
  • RNA polymerase binds successfully, allowing transcription.

Concept of Regulons

• Definition:
  • Groups of operons controlled by a single regulatory protein.
  • MALT can bind to multiple activator sites, influencing various operons.

Key Terms

• Positive Control: Transcription relies on activator proteins.
• Effector Molecule: Induces conformational change in activator proteins.
• Regulon: Multiple operons regulated by the same protein.
• DNA Looping: Mechanism allowing distant activator binding sites to influence transcription.

Summary

• Positive control is crucial for efficient transcription in certain operons.
• The presence of specific molecules (e.g., maltose) is essential for activator proteins to enable RNA polymerase binding.