Which of the following is an example of a regulatory element in eukaryotes?

• A. Coding region
• B. Operator
• C. Start codon
• D. TATA box

Answer: (D)

Regulatory elements control when a gene is transcribed and how much mRNA is produced. In eukaryotes, a key regulatory element is the TATA box, a promoter sequence that sits just upstream of where transcription starts. It helps position RNA polymerase II by binding the TATA-binding protein, a component of the transcription factor complex TFIID, which then enables the assembly of the full transcription machinery. This arrangement is essential for initiating transcription.

The other options aren’t regulating transcription in eukaryotes: the coding region is the part that is transcribed and translated into a protein; an operator is a bacterial regulatory site not used in eukaryotic genomes; and the start codon marks where translation begins and is part of the coding sequence rather than a regulatory DNA element.