Question

As regards transcription, the prototype enhancer discovered in the animal virus SV40 is a sequence of __________ base pairs.

• A. 7
• B. 72
• C. 27
• D. 127

Hint:

This classic viral enhancer is remembered specifically as a repeated segment of this length.

Answer 1

The Correct Option is B

Step 1: Before enhancers were understood as a distinct class of regulatory DNA elements, researchers studying SV40, a small DNA tumour virus, noticed a segment upstream of its early genes that dramatically increased transcription even when moved or flipped in orientation.

Step 2: This segment turned out to be a repeated 72 base pair sequence, and its discovery established the defining features of enhancers as position- and orientation-independent boosters of gene expression.

Step 3: Since this specific 72 bp repeat is the historically recognised prototype enhancer, the correct answer is 72.