Domain architecture of eukaryotic transcriptional activators: They usually contain which structural features?
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AAt least two distinct domains: a DNA-binding domain and an activation domain
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BOnly a DNA-binding domain without any activation region
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CAt least two domains and a DNA-binding domain (but no activation domain)
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DNo modular structure; they are single-domain proteins
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EOnly chromatin-binding without sequence specificity
Answer
Correct Answer: At least two distinct domains: a DNA-binding domain and an activation domain
Explanation
Introduction / Context: Many eukaryotic transcriptional activators are modular proteins that bind specific DNA sequences and recruit coactivators or the basal transcription machinery to enhance gene expression.
Given Data / Assumptions:
- Activators typically have separable domains.
- DNA-binding and activation functions can be experimentally reassorted.
Concept / Approach: A canonical activator includes a DNA-binding domain (zinc finger, bZIP, bHLH, etc.) and an activation domain (acidic, glutamine-rich, proline-rich) that interacts with coactivators such as Mediator or histone-modifying enzymes.
Step-by-Step Solution: Identify the minimal modular requirement → DNA-binding + activation. Exclude options lacking activation capacity or modularity. Select the statement reflecting two-domain architecture.
Verification / Alternative check: Domain-swap experiments show that activation domains can function when fused to unrelated DNA-binding domains.
Why Other Options Are Wrong: Options without activation domains cannot stimulate transcription; claiming no modularity contradicts extensive biochemical data.
Common Pitfalls: Confusing activation domains with general transcription factors; overlooking coactivator recruitment.
Final Answer: At least two distinct domains: a DNA-binding domain and an activation domain.