A reporter gene assay uses a regulatory sequence to drive expression of a detectable gene; which of the following is commonly used as a reporter gene?

• A. GFP
• B. Luciferase
• C. Beta-galactosidase
• D. Chloramphenicol acetyltransferase

Answer: (C)

Reporter gene assays quantify regulatory sequence activity by linking it to a gene whose product gives a detectable signal. Beta-galactosidase is a classic choice because its enzymatic activity can be measured easily with simple substrates that produce a color change or a measurable absorbance, such as X-gal yielding a blue color or ONPG producing a yellow signal. This makes it straightforward to compare promoter strength across many samples in a robust, inexpensive readout. Other reporters like GFP or luciferase are also useful and offer live-cell fluorescence or high sensitivity, but historically beta-galactosidase has been the most widely used due to its simple, reliable, and inexpensive colorimetric assays.