GAL4/UAS system

The GAL4-UAS system is a biochemical method used to study gene expression and function in organisms such as the fruit fly.

It is based on the finding by Hitoshi Kakidani and Mark Ptashne,[1] and Nicholas Webster and Pierre Chambon[2] in 1988 that Gal4 binding to UAS sequences activates gene expression.

The method was introduced into flies by Andrea Brand and Norbert Perrimon in 1993[3] and is considered a powerful technique for studying the expression of genes.

Geneticists have created genetic variants of model organisms (typically fruit flies), called GAL4 lines, each of which expresses GAL4 in some subset of the animal's tissues.

For example, GAL4/UAS-regulated transgenes in Drosophila have been used to alter glial expression to produce arrhythmic behavior in a known rhythmic circadian output called pigment dispersing factor (PDF).

[8] However, some research has indicated that over-expression of GAL4 in Drosophila can have side-effects, probably relating to immune and stress responses to what is essentially an alien protein.

[9] The GAL4-UAS system has also been employed to study gene expression in organisms besides Drosophila such as the African clawed frog Xenopus[10] and zebrafish.

When combined with intrinsically sparse GAL4 lines, this offers very specific selection, often limited to a single cell type.