How can a fusion protein reporter be used to monitor expression in cells?

• A. It destroys protein function to measure degradation
• B. A fluorescent or luminescent tag fused to the protein enables visualization or quantification of expression
• C. It labels DNA instead of protein
• D. It increases transcription without reporting expression

Answer: (B)

Fusion protein reporters work by attaching a detectable tag to the protein of interest. The tag—such as GFP, mCherry, or luciferase—emits fluorescence or light when the fusion protein is produced. By measuring the emitted signal with a microscope, plate reader, or flow cytometer, you get a direct readout of how much protein is being made and where it is located in the cell. This lets you monitor expression dynamics over time, compare different conditions, and quantify expression levels because the signal intensity correlates with the amount of fusion protein present. While the fusion is designed to report expression with minimal disruption to function, it's important to consider potential interference from the tag. Other options described don’t provide a direct visualization or quantification of protein expression: they either imply degrading the protein, labeling DNA, or increasing transcription without reporting the actual expression level.