UASG in GAL genes functions as:
UASG contains four 17-base-pair palindromic sites for Gal4 dimer located 200-400 nucleotides upstream of GAL1/GAL10 shared TATA box. Functionally analogous to metazoan enhancer, UASG activates heterologous promoters irrespective of orientation, requires Mediator and SAGA for looped communication with basal promoter via DNA bending. When fused to CYC1 minimal promoter driving reporter, UASG confers strong galactose inducible expression, classic enhancer test. Although yeast lacks distal enhancer complexity, UASG exemplifies enhancer concept in simple eukaryote, demonstrating activator recruitme
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 7: UASG as Enhancer Element in Yeast GAL System
