What is the primary purpose of a reporter gene assay?

• A. Diagnose genetic mutations
• B. Measure DNA replication rate
• C. Measure regulatory sequence activity
• D. Determine protein folding

Answer: (C)

A reporter gene assay is used to quantify how a regulatory DNA sequence controls gene expression by producing a measurable output from a linked reporter gene. In this setup, a regulatory element such as a promoter or enhancer is placed in front of a reporter gene (like luciferase, GFP, or beta-galactosidase). When the regulatory element drives transcription, the reporter gene is expressed and its product is easy to detect and quantify. The amount of signal reflects how active the regulatory sequence is under the tested conditions, allowing comparisons of different elements, mutations, or treatments.

This approach directly measures transcriptional control, which is why it best fits the purpose of assessing regulatory sequence activity. It’s not used to diagnose genetic mutations by itself, nor to measure DNA replication rates, nor to determine protein folding, all of which involve different assays and readouts.