Histone Acetyltransferase Complexes Can Mediate Transcriptional Activation by the Major Glucocorticoid Receptor Activation Domain

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Abstract
Previous studies have shown that the Ada adapter proteins are important for glucocorticoid receptor (GR)-mediated gene activation in yeast. The N-terminal transactivation domain of GR, τ1, is dependent upon Ada2, Ada3, and Gcn5 for transactivation in vitro and in vivo. Using in vitro techniques, we demonstrate that the GR-τ1 interacts directly with the native Ada containing histone acetyltransferase (HAT) complex SAGA but not the related Ada complex. Mutations in τ1 that reduce τ1 transactivation activity in vivo lead to a reduced binding of τ1 to the SAGA complex and conversely, mutations increasing the transactivation activity of τ1 lead to an increased binding of τ1 to SAGA. In addition, the Ada-independent NuA4 HAT complex also interacts with τ1. GAL4-τ1-driven transcription from chromatin templates is stimulated by SAGA and NuA4 in an acetyl coenzyme A-dependent manner. Low-activity τ1 mutants reduce SAGA- and NuA4-stimulated transcription while high-activity τ1 mutants increase transcriptional activation, specifically from chromatin templates. Our results demonstrate that the targeting of native HAT complexes by the GR-τ1 activation domain mediates transcriptional stimulation from chromatin templates.