reporter genes

Meaning: A reporter gene is a gene whose product is easy to see or measure. Researchers place it under the control of the promoter or enhancer being studied, or fuse it to the coding sequence of a protein of interest. When the regulatory sequence is active, the reporter is transcribed and translated, and the signal reports that activity. GFP fluoresces under blue or UV light and lets researchers watch a protein's location in living cells. LacZ encodes β-galactosidase, which cleaves X-gal to a blue product. Luciferase produces light when given its substrate, luciferin.

On the MCAT: A passage may fuse a promoter to GFP, then add an inducer or delete a transcription factor binding site. You predict the change in fluorescence: a deleted activator site lowers the signal, and a deleted repressor site raises it. Another version fuses GFP to a protein to see whether it sits in the nucleus, cytoplasm, or membrane. Blue-white screening is also common: a insert that disrupts lacZ gives white colonies on X-gal, while an intact lacZ gives blue colonies.

Common confusion: The reporter is not the gene under study. It measures the activity of the regulatory region or the location of the tagged protein. No signal means the promoter was inactive under those conditions or in that cell type, or that the construct failed. It does not by itself prove the native gene is absent.