Gene Regulation in Eukaryotes

Overview

This section explains how gene expression in eukaryotes is regulated during transcription by transcription factors, promoters, enhancers, and repressors.

Transcription Factors and Gene Regulation

• Eukaryotic RNA polymerase cannot initiate transcription without other proteins called transcription factors.
• General (basal) transcription factors bind to the core promoter to help RNA polymerase start transcription.
• Specific transcription factors bind to sites outside the core promoter to enhance or repress RNA polymerase activity.

The Promoter and Transcription Machinery

• Promoter regions are upstream of coding sequences and bind transcription factors needed for transcription initiation.
• The TATA box, found 25-35 bases upstream, is a core promoter element where the TFIID protein complex binds.
• TFIID recruits other transcription factors like TFIIB, TFIIE, TFIIF, and TFIIH, which help assemble the transcription initiation complex.
• Additional core promoter-proximal elements, like the CAAT box and GC box, provide more binding sites for specific transcription factors.
• Transcription factors that bind promoter regions are called cis-acting elements because they are on the same chromosome as the gene.

Enhancers and Transcription

• Enhancers are DNA regions that increase transcription, sometimes located far from the gene they regulate.
• Enhancers provide binding sites for specific transcription factors (activators), which, when bound, can interact with promoter-bound proteins.
• DNA bending proteins facilitate contact between enhancer-bound activators and the promoter region, enabling efficient transcription.
• Different genes can have distinct enhancer elements, allowing for differential gene expression.

Turning Genes Off: Transcriptional Repressors

• Transcriptional repressors bind to promoter or enhancer regions to block transcription.
• Repressors prevent the binding of activating transcription factors in response to external stimuli.

Key Terms & Definitions

• Transcription factor — Protein that regulates transcription by binding to specific DNA sequences.
• General transcription factor — Protein that binds to the core promoter to help RNA polymerase initiate transcription.
• Specific transcription factor — Protein that binds outside the core promoter to enhance or repress transcription.
• Promoter — DNA sequence upstream of a gene that regulates transcription initiation.
• TATA box — DNA sequence in the promoter where TFIID binds to start transcription.
• Enhancer — Distant DNA region that increases transcription when bound by activators.
• Repressor — Protein that binds DNA to inhibit gene transcription.
• Cis-acting element — DNA sequence near a gene that regulates its transcription on the same chromosome.

Action Items / Next Steps

• Review examples of eukaryotic promoters, enhancers, and repressors.
• Practice identifying transcription factors and their binding sites in gene diagrams.