Enhancer trap

In essence, enhancer traps are transgenic constructions by the fusing of two proteins that are inserted into the genome for the identification of enhancers. Its structure contains a mobile element (necessary for random insertion in the genome) usually some sort of P element (a promoter that must be sensitive to the enhancer) and a reporter gene. The reporter gene is necessary for identification of the spatial regulation by enhancers. The most common and basic enhancer traps are: P [ lacZ ] from bacterium E.coli and P [GAL4] from yeast.

The enhancer trap also uses some sort of visible marker that allows the new insertions to be recognized such as the white eye color gene in Drosophila or ampicillin resistance for E. coli.

In fruit flies (Drosophila), there exists a large number of flies containing GAL4 insertions and an equally large number of flies containing a UAS DNA sequence followed by a gene of interest. The beauty of this arrangement is that the expression of a large number of genes with different GAL4 "drivers" is possible. Rather than generating transgenic flies with the enhancer linked directly to the gene of interest (this takes about a year, if you are starting without the appropriate DNA construct), you simply mate (cross) one trangenic fly with another transgenic fly.

References

A. Brand and N. Perrimon (1993). Targeted gene expression as a means of altering cell fates and generating dominant phenotypes. Development, 118, pp 401-415. [

[D. J. Finnegan (1992). Transposable elements. Current Opinion in Genetics and Development, 2, pp 861-867. [

J. A. Fischer, E. Giniger, T. Maniatis and M. Ptashne (1988). GAL4 activates transcription in Drosophila. Nature, 332, pp 853-856.]