630 Microbiology for Teachers

Regulation of Gene Expression

Specific Regulation

• Negative 

   

  • induction

   

  • binding of an inducer

   

  • inhibits repressor binding to the operator

   

  • RNA polymerase now binds to the promoter

   

  • repression

   

  • repressor-corepressor complex binds to the operator

   

  • RNA polymerase progression to the start site is inhibited

   

  • gene transcription is inhibited

   

• positive

   

  • inducer (generally the substrate) binds to an activator protein

   

  • activator now binds to the activator site

   

  • activator interacts with RNA polymerase

   

  • RNA polymerase binds the promoter

   

Attenuation

Attenuation used to regulate biosynthetic pathways (especially those for amino acids essential metabolites that need precise level control) and is accomplished as follows:

• Abundance of the biosynthetic product

   

• Cleavage of the nascent protein generates an attenuator peptide

   

• Attenuator peptide interacts with mRNA

   

• Stem-loop structure slows down (attenuates) transcription

   

Global Regulation

Global regulation is simultaneous regulation of a large number of unrelated genes or gene products

• Catabolite repression
  • Mechanism

   

   

  • Glucose regulation

   

   

• Proteases

   

• Chaperonins