Activation of the ADE Genes Requires the Chromatin Remodeling Complexes SAGA and SWI/SNF

The activation of theADE regulon genes requires the pair of transcription factors Bas1 and Pho2. In a genome-wide screen for additional regulators of the pathway, strains with mutations in multiple subunits of the chromatin remodeling complexes SAGA and SWI/SNF were uncovered. These mutants exhibited decreased expression of anADE5,7-lacZ reporter and nativeADE compared to the wild-type strains, but the expression of theBAS1 andPHO2 genes was not substantially decreased. An unregulated Bas1-Pho2 fusion protein depended upon SAGA and SWI/SNF activity to promote transcription of a reporter. A significant but low-level association of Gcn5-myc and Snf2-myc with theADE5,7 promoter was independent of adenine growth conditions and independent of the presence of the activator proteins Bas1 and Pho2. However, the increase in occupancy of Bas1 and Pho2 atADE5,7 depended on both SAGA and SWI/SNF. The loss of catalytic activity of both SAGA and SWI/SNF complexes in thegcn5 Δsnf2 Δ double mutant was severely detrimental toADE-lacZ reporter expression and nativeADE gene expression, indicating complementary roles for these complexes. We conclude that Bas1 and Pho2 do not recruit the SAGA and SWI/SNF complexes to theADE5,7 promoter but that the remodeling complexes are necessary to increase the binding of Bas1 and Pho2 in response to the adenine regulatory signal. Our data support the model that the SAGA and SWI/SNF complexes engage in global surveillance that is necessary for the specific response by Bas1 and Pho2.