*14 - Transcription

• Cells may require different amounts of certain proteins at different times
• Cells regulate transcription because:

  • Cells require different amounts of different proteins
  • Some cells may only need certain proteins at certain times
  • Some cells in multicellular organisms only need to produce a subset of proteins encoded by the genome
• Transcription factors contain a DNA binding domain and a transactivating domain
• 10% of the human genome codes for transcription factors
• Transcription factors are proteins that regulate transcription
• Helix-turn-helix domains are found in all types of organisms
• Coiled coil domains are found in leucine zipper and helix-loop-helix motifs
• Zinc finger domains are very common in humans
• Examples of DNA binding domains of TFs:

  • Helix-turn-helix
  • Coiled coil
  • Zinc finger
• In prokaryotes, the RNA polymerase holoenzyme can transcribe any gene with a functional promoter
• Targeted gene regulation is used mostly at:

  • Transcription initiation (most often)
  • Elongation / Termination
  • Regulation from the transcribed RNA itself
• Repressors are regulatory proteins that decrease transcription
• Activators are proteins that increase transcription
• Operators are regulatory DNA sequences that activators and repressors bind to
• Enhancers increase transcription
• Silencers decrease transcription
• Distal (1000s bp) regulatory sequences are found in eukaryotes - called enhancers - which can be up or downstream of the gene
• In eukaryotes, regulatory sequences frequently bind several regulatory proteins to allow expression to be tuned
• Operons are common in bacteria but rare in eukaryotes (?)