It is true that all GAL structural genes have UAS elements in their enhancer regions.
UAS elements can be found in the enhancer regions of every GAL structural gene. An enhancer is a short portion of DNA (50–1500 bp) that can be bound by proteins (activators) to increase the likelihood of a particular gene being transcribed.
The GAL4-UAS system is a biochemical technique used to investigate gene expression and function in fruit flies. Two parts make up the system: the Gal4 protein, which is an activator of transcription in yeast, and the UAS (Upstream Activation Sequence), which is an enhancer to which GAL4 binds specifically to initiate transcription.
