Eukaryotic Transcription Overview

Eukaryotic Transcription

• RNA polymerase is the enzyme responsible for transcription

  • Prokaryotes have one RNA polymerase enzyme
  • Eukaryotes have three RNA polymerase enzymes
  • RNA Polymerase II is responsible for transcribing mRNA

• Transcription Factors are proteins required for transcription initiation

  • Designated as TF (transcription factor)
  • TFII indicates a transcription factor for RNA Polymerase II
  • The letter following TFII indicates the specific function
  • Examples:
    • TFIIA
    • TFIIB
    • TFIID
    • TFIIE
    • TFIIF
    • TFIIH

Transcription Initiation

• TFIIB binds to the TATA element (Tata box) within the promoter
  • The promoter is approximately 40 nucleotides long upstream and downstream of the transcription start site.
  • The TATA element is 80 nucleotides upstream of the transcription start site.
• TFIID contains TBP (TATA Binding Protein), which binds to the TATA sequence
  • Bends DNA by 80 degrees
  • This bending aids in the binding of other transcription factors
• TFIIE stabilizes TFIID binding to the promoter.
• TFIIF interacts with TBP and the promoter downstream of the TATA element, assisting RNA polymerase II recruitment to the promoter.
• TFIIF binds the promoter with RNA polymerase II, enabling RNA polymerase II recruitment.
• TFIIE assists in the formation of the pre-initiation complex
• TFIIH is a large complex with 9 subunits
  • Two subunits possess ATPase activity
    • Functioning as helicase, TFIIH melts the promoter
    • Transitions the pre-initiation complex to the open complex
  • Seven subunits exhibit kinase activity
    • Phosphorylates the C-terminal domain (CTD) of RNA Polymerase II
    • Initiates promoter escape and transcription elongation

Transcription Elongation

• Elongation Factors aid in transcription elongation
  • TFIIE is recruited by transcription activators
  • Phosphorylates serine residues on the CTD of polymerase, stimulating elongation
  • TFIIE regulates transcription rate
    • Varied rate at different DNA sequences
    • Prevents polymerase pausing and encourages movement

5' Capping

• Occurs during elongation
• Protection and mRNA ribosome recruitment
  • Occurs 5' to 3'
  • RNA triphosphatase removes terminal gamma phosphate
  • Guanine transferase attaches guanine to the beta phosphate of the first nucleotide
  • Methyl transferase adds a methyl group to the guanine nucleotide
  • This 5' cap enables mRNA ribosome recruitment for translation initiation

Transcription Termination

• RNA Polymerase II's CTD interacts with CSTF (Cleavage Stimulation Factor) and CPSF (Cleavage and Polyadenylation Specificity Factor)
• These proteins are recruited to the mRNA at the gene end by the CTD
• CSTF leaves the mRNA after cleavage
• CPSF recruits Poly(A) polymerase
  • Adds ~200-250 adenine residues to the 3' end, forming the poly(A) tail
  • Uses ATP
• Poly(A) binding protein binds the poly(A) tail, preventing degradation
• CPSF is released from the mRNA