General transcription factors (GTFs) are a group of essential proteins that help initiate transcription by assembling at the core promoter of protein-coding genes and recruiting RNA polymerase II. They are required for basal (basic) transcription of almost all genes in eukaryotic cells.
🔑 Definition:
General transcription factors (GTFs) are core regulatory proteins that form part of the pre-initiation complex (PIC) and enable RNA polymerase II to bind to DNA and start transcription.
🧱 The Major GTFs (for RNA Polymerase II):
| GTF Name | Function |
|---|---|
| TFIID | First to bind; contains TBP (TATA-binding protein) and TAFs; recognizes the promoter |
| TFIIA | Stabilizes TFIID-DNA interaction |
| TFIIB | Positions RNA polymerase II at the transcription start site |
| TFIIF | Escorts RNA polymerase II to the complex and stabilizes the assembly |
| TFIIE | Recruits and regulates TFIIH |
| TFIIH | Unwinds DNA (helicase activity) and phosphorylates RNA Pol II (kinase activity) |
🔄 Step-by-Step Role of GTFs in Transcription Initiation:
- TFIID binds to the TATA box (or another core promoter element) via TBP.
- TFIIA and TFIIB join in to help stabilize and position the complex.
- TFIIF brings in RNA polymerase II.
- TFIIE binds and recruits TFIIH.
- TFIIH:
- Unwinds DNA (so it can be read)
- Phosphorylates RNA Pol II’s CTD, triggering transcription to begin
Once these components are in place, the pre-initiation complex (PIC) is complete, and transcription can start.
📦 Why Are GTFs Important?
| Role | Importance |
|---|---|
| Essential for all transcription | Without GTFs, RNA polymerase II cannot begin transcription |
| Gene regulation | Their activity can be modulated by activators, repressors, or signaling pathways |
| Precision control | Help ensure genes are expressed at the right time, place, and level |
🧠 Difference from Specific Transcription Factors:
| Feature | General Transcription Factors (GTFs) | Specific Transcription Factors |
|---|---|---|
| Required for all genes? | Yes (core machinery) | No (gene-specific) |
| Bind to? | Core promoter (e.g., TATA box) | Enhancers or silencers (far from the gene) |
| Function | Start transcription | Increase or decrease transcription levels |
📌 Summary:
General transcription factors are the essential “starter proteins” that assemble with RNA polymerase II at a gene’s promoter to begin transcription. They form the core machinery used by all cells to transcribe DNA into RNA and are a fundamental part of gene expression.