One important tool in molecular biology takes advantage of promoter fusions where the expression of one gene is controlled by the promoter or regulatory elements of another gene. Promoter fusions engineered in vitro can help to determine how gene expression is regulated in cells and whole organisms. Promoter fusions generated in vivo, for example by promoter trapping, can help to identify new genes and generate useful genetic resources for dissecting important biological processes. A binary effector–reporter system can be used to direct the production of a protein of interest in specific cells of an organism for functional studies. It can also be used to direct the production of interference ribonucleic acid molecules that can inhibit the activity of their target genes in specific cells of an organism. The GAL4–UAS version of this binary system is a valuable genetic tool for investigations of mechanisms that control development.
