Question

For each of the following transcription factors, explain how eukaryotic transcriptional initiation would be affected if it were missing. A. TFIIB C. TFIIH B. TFIID

Short answer

TFIIB helps in positioning RNA polymerase II for transcription initiation. Without it, the initiation would likely fail. TFIID binds to the TATA box and initiates the assembly of the transcription complex. Each absence would lead to compromised transcription initiation. TFIIH unwinds the DNA and phosphorylates RNA Polymerase II to start elongation, its absence would affect both these steps, greatly affecting transcription initiation.

Step-by-step solution

Role of TFIIB in transcription initiation

TFIIB binds to the TFIID/TATA box complex and helps recruit RNA polymerase II and other factors necessary for transcription. It essentially helps position the polymerase properly for transcription initiation. If TFIIB were missing, RNA polymerase II wouldn't be positioned accurately and thus transcription initiation would likely fail.

Role of TFIID in transcription initiation

TFIID is a protein complex that binds to the TATA box within the promoter region of the gene. This initiates the assembly of other transcription factors and RNA polymerase II at the start site of the gene segment to be transcribed. If TFIID were missing, the assembly of the transcription complex would be compromised, inhibiting transcription initiation.

Role of TFIIH in transcription initiation

TFIIH has two main functions in transcription initiation. It unwinds the DNA around the transcription start site (creating a transcription bubble) and phosphorylates the Serine 2 residues in the carboxy-terminal domain (CTD) of RNA Polymerase II, enabling the polymerase to clear the promoter and start elongation. If TFIIH were missing, the DNA wouldn't unwind to create the transcription bubble and RNA Polymerase II wouldn't start elongation, and thus transcription initiation would greatly be affected.