A gene (R) that (1) can generate a product which is easy to visualize and (2) can respond to a regulatory signal meant for a second gene. It is this gene (X) that is of primary interest, but there may be no convenient method of recording its activity. The tissue-specific expression of gene X can be monitored by letting the R gene intercept a regulatory signal meant for X. R responds by synthesizing its product and thus “reports” the time and place of activation of X. The lac Z gene of E. coli has been used extensively as a reporter. Its product is beta galactosidase. This enzyme normally breaks down lactose, but under the conditions of the experiment an analog of lactose is provided. When this compound (5-bromo-4-chloro-indolyl-β-d-galactoside) is cleaved by beta galactosidase, it yields 5-bromo-4-chloro- indigo, a blue dye. The production of this blue pigment in a particular tissue during development reports the activation of the gene under study. See enhancer trap, lac operon.
Subjects: Genetics and Genomics.