Figure 6.

ZIPIC mediates long-distance activation of a promoter by GAL4 in yeast. (A) Structure of the his gene reporter system to monitor ZIPIC activity in yeast. Ten GAL4 binding sites (G4) were inserted at the 3′ end of the his gene. The DNA fragments containing three ZIPIC sites (indicated as black circles) were inserted in reverse orientation upstream of the his promoter and downstream of the GAL4 binding sites. (B) Expression of ZIPIC promotes transcriptional activation at large distances. The reporter construct depicted in (A) was integrated into the genome. Expression of the his reporter was spot-assayed by measuring colony formation on plates containing the 3-amino-1,2,4-triazole (3-AT): the higher the concentration of 3-AT, the higher the level of HIS3 protein required for growth (97). (C) Mutant ZIPIC protein lacking the ZAD domain fails to support long-distance activation by GAL4.