The promoter region of the operon that encodes various proteins involved in galactose metabolism, including *β-galactosidase (‘beta-gal’). The operon is inducible and once β-galactosidase is expressed it will act on the chromogenic substrate Xgal to produce a blue colour. This colour change is a convenient marker of colonies that have been transformed by a vector carrying the beta-gal gene. Both yeast and bacterial forms of the promoter are used experimentally and GAL4, the heterodimeric yeast transcription factor that binds to the UASG (upstream activation site G) promoter, is commonly used in yeast two-hybrid screening.
Subjects: Medicine and Health.