Which of the following is an example of a cis-acting element in eukaryotic transcription?

• A. RNA polymerase
• B. Enhancer
• C. Mediator complex
• D. Transcription factor

Answer: (B)

Verified step by step guidance

1. Understand the concept of cis-acting elements: Cis-acting elements are regions of non-coding DNA which regulate the transcription of nearby genes. They are typically located on the same molecule of DNA as the gene they regulate.
2. Identify the role of enhancers: Enhancers are a type of cis-acting element. They are sequences of DNA that can increase the rate of transcription of a gene. Enhancers can be located upstream, downstream, or even within the gene they regulate.
3. Differentiate between cis-acting and trans-acting elements: Trans-acting elements, such as transcription factors and RNA polymerase, are proteins that bind to cis-acting elements to regulate gene expression. They are not part of the DNA sequence itself.
4. Evaluate the options given: RNA polymerase and transcription factors are trans-acting elements because they are proteins that interact with DNA to regulate transcription. The mediator complex is also a protein complex involved in transcription regulation.
5. Conclude that the enhancer is the correct example of a cis-acting element: Since enhancers are DNA sequences that regulate transcription from the same molecule of DNA, they fit the definition of cis-acting elements.