A reporter gene is a type of gene that facilitates the detection or quantification of gene expression. Reporter genes play a key role in a wide range of in-vitro and in-vivo applications. Also known as small reporter proteins or protein expression markers, they are often used as indicators of transcriptional activity in cells and to analyze cis-acting transcriptional elements. Reporter genes also play important roles in regulating translation and transcription, processing mRNA, identifying and characterizing promoter and enhancer elements, monitoring DNA delivery methods, and studying protein-protein interactions.