Reporter gene

A reporter gene encodes a protein that makes its presence obvious, by fluorescing, giving off light or producing a color. Researchers link it to a piece of DNA they want to study, so the reporter's signal stands in for something harder to observe directly, such as whether a promoter is active, where a protein goes in the cell or whether a plasmid has entered a host.

Common reporters include green fluorescent protein (GFP), first taken from a jellyfish, and its colored relatives, which glow under blue or ultraviolet light without any added chemical and so suit living cells; firefly luciferase, a very sensitive reporter that emits light when given its substrate, luciferin; and the bacterial lacZ gene, whose enzyme, beta-galactosidase, turns the colorless compound X-gal blue. To measure a promoter, the reporter's coding sequence is placed just downstream of it, so the strength of the signal reflects how actively the promoter drives transcription. Alternatively, the reporter can be fused to a protein to follow where that protein goes.

Students meet reporter genes in blue-white screening of cloned plasmids, in transgenic organisms that glow under ultraviolet light and in drug-screening assays. In synthetic biology, fluorescent reporters are the standard way to measure the output of genetic circuits.