Eukaryotic Transcription Lecture Notes

Overview

• Eukaryotic transcription involves the synthesis of mRNA from DNA.
• Enzyme required: RNA Polymerase.
• Prokaryotes have one RNA polymerase; eukaryotes have three (I, II, and III).
• RNA Polymerase II is crucial for mRNA transcription in eukaryotes.

Key Components

• Transcription Factors (TFs)
  • General transcription factors assist RNA Polymerase II.
  • Designation: TFII (Transcription Factor for RNA Polymerase II) followed by letters A, B, D, E, F, and H based on specific functions.
  • Mnemonics for TFs:
    • TFIID: Dog
    • TFIIE: Elephant
    • TFIIF: Football
    • TFIIH: Helicopter

Transcription Initiation

• Promoter and TATA Box

  • Promoter is ~40 nucleotides long.
  • TATA Box located ~30 nucleotides upstream.
  • TATA-binding protein (TBP) is part of TFIID and binds the TATA sequence.
  • Binding of TBP bends DNA, facilitating the recruitment of other TFs.

• Sequence of Events

  1. TFIID binds TATA box.
  2. TFIIA stabilizes TFIID binding.
  3. TFIIB interacts with TBP and recruits RNA Polymerase II.
  4. TFIIF assists RNA Polymerase II to bind the promoter.
  5. TFIIE recruits TFIIH.
  6. TFIIH has ATPase and kinase activities, facilitating promoter melting and elongation.

Transcription Elongation

• Transition to Elongation Phase
  • After initiation, RNA Polymerase II shifts to elongation.
  • Elongation factors: TFEb and TFIIS.
  • TFEb is a kinase that phosphorylates the C-terminal domain of RNA Polymerase II, enhancing elongation.
  • TFIIS prevents RNA Polymerase pausing and enhances transcription rate.

RNA Processing

• 5' Capping
  • Occurs during elongation.
  • Involves three steps:
    1. Removal of terminal gamma phosphate by RNA triphosphatase.
    2. Addition of guanine by guanylyltransferase.
    3. Methylation of guanine by methyltransferase.
  • Resulting 5' cap is crucial for mRNA translation initiation.

Termination of Transcription

• Occurs when RNA Polymerase reaches the end of the gene.

• Key Proteins Involved

  • CstF: Cleavage stimulation factor.
  • CPSF: Cleavage and polyadenylation specificity factor.

• Process

  1. CstF and CPSF are recruited by the C-terminal domain of RNA Polymerase II.
  2. mRNA is cleaved; CstF dissociates.
  3. CPSF facilitates polyadenylation by recruiting poly(A) polymerase.
  4. Poly(A) polymerase adds ~200 adenine residues, forming the poly(A) tail.
  5. Poly(A) binding protein binds the tail, preventing degradation.

• Mnemonic for transcription initiation steps: "The dog eats the apple and plays with the football, he gets tired and sits in front of the fan, when he sees an elephant he runs away in the helicopter."