Overview
This lecture covers how gene expression is regulated at the level of transcription in eukaryotes, focusing on the roles of transcription machinery and transcription factors.
Review of Transcription
- Transcription is the process where DNA is read to produce messenger RNA (mRNA).
- In eukaryotes, pre-mRNA is made by RNA polymerase II.
- RNA polymerase II requires transcription factors to initiate transcription.
- Transcription factors bind to the promoter region upstream of the gene.
Types of Transcription Factors
- General (basal) transcription factors bind to the core promoter to recruit RNA polymerase.
- Specific transcription factors bind to DNA regions outside the core promoter and can enhance or repress transcription.
- The TATA box, a DNA sequence in the promoter, is where the first general transcription factor (TFIID) binds.
- TFIID contains the TATA-binding protein and recruits additional transcription factors and RNA polymerase, forming the transcription initiation complex.
Promoter Proximal and Distal Elements
- Promoter proximal elements are near the promoter and bind cis-acting elements (transcription factors acting nearby).
- Enhancer regions, containing distal control elements, are far upstream and bind activators.
- DNA bending proteins and mediator proteins bring enhancers close to the promoter so activators interact with transcription factors, enhancing transcription.
Gene-Specific Expression in Different Cell Types
- Most body cells have all genes, but only specific genes are expressed in each cell type.
- Different genes can share the same promoter but have different distal control elements in their enhancers.
- Activator proteins, specific to cell type, bind to these control elements to regulate gene expression.
- Only genes with matching activators in a given cell will be transcribed.
Key Terms & Definitions
- Transcription — process of copying DNA into RNA.
- Promoter — DNA region upstream of a gene where transcription factors bind.
- TATA box — a promoter DNA sequence recognized by TFIID.
- General (basal) transcription factors — proteins needed for RNA polymerase binding to the promoter.
- Specific transcription factors — proteins affecting transcription from distant DNA elements.
- Promoter proximal elements — regulatory DNA sequences near the promoter.
- Enhancer — DNA region far from the promoter, containing distal control elements for gene regulation.
- Cis-acting elements — DNA sequences and factors affecting nearby genes.
- Activator — protein binding to enhancer elements to increase transcription.
- Mediator proteins — proteins enabling communication between activators and the transcription machinery.
Action Items / Next Steps
- Review provided YouTube videos for visual explanations of transcription factor interactions.
- Prepare for the next lecture on post-transcriptional regulation, protein stability, and gene expression in cancer.