Enhancers versus promoters: Which distinguishing feature is correct about enhancer elements?

Introduction / Context:
Enhancers are distal regulatory DNA sequences that increase transcription from target promoters. Unlike core promoters, enhancers operate flexibly with respect to position and orientation via DNA looping and co-activator recruitment.

Given Data / Assumptions:

• Enhancers bind transcriptional activators and co-activators.
• They can act at long distances, upstream, downstream, or within introns.
• Enhancers do not directly serve as RNA polymerase initiation sites.

Concept / Approach:
A hallmark of enhancers is orientation independence: the sequence can be inverted and still function. Promoters, by contrast, are direction-specific and position-constrained relative to the transcription start site.

Step-by-Step Solution:
Identify enhancer properties: position/orientation independence, TF binding, looping to promoters.Reject statements implying direct initiation or strict adjacency requirements.Select the correct distinctive feature: orientation can be inverted without effect.

Verification / Alternative check:
Reporter constructs demonstrate retained activity upon enhancer inversion, while promoter inversion abolishes initiation.

Why Other Options Are Wrong:

• Initiate transcription / bind polymerase: Promoter function, not enhancer.
• Adjacent to start codon: Enhancers can be far away.
• Restricted to one gene/position: Enhancers can target multiple promoters depending on context and chromatin architecture.

Common Pitfalls:
Equating all regulatory elements; promoters and enhancers have distinct directionality and roles.

Final Answer:
Their orientation can be inverted with little or no effect on function.