ADR1 ACTIVATION DOMAINS CONTACT THE HISTONE ACETYLTRANSFERASE GCN5 AND THE CORE TRANSCRIPTIONAL FACTOR TFIIB

The yeast transcriptional activator ADR1, which is required for ADH2 a nd peroxisomal gene expression, contains four separable and partially redundant activation domains (TADs), Mutations in ADA2 or GCN5, encodi ng components of the ADA coactivator complex involved in histone acety lation, severely reduced LexA-ADR1-TAD activation of a LexA-lacZ repor ter gene, Similarly, the ability of the wild-type ADR1 gene to activat e an ADH2-driven promoter was compromised in strains deleted for ADA2 or GCN5, In contrast, defects in other general transcription cofactors such as CCR4, CAF1/POP2, and SNF/SWI displayed much less or no effect on LexA-ADR1-TAD activation, Using an in vitro protein binding assay, ADA2 and GCN5 were found to specifically contact individual ADR1 TADs , ADA2 could bind TAD II, and GCN5 physically interacted with all four TADs, Both TADs I and IV were also shown to make specific contacts to the C-terminal segment of TFIIB, In contrast, no significant binding to TBP was observed, TAD IV deletion analysis indicated that its abili ty to bind GCN5 and TFIIB was directly correlated with its ability to activate transcription in vivo, ADR1 TADs appear to make several conta cts, which may help explain both their partial redundancy and their va rying requirements at different promoters, The contact to and dependen ce on GCN5, a histone acetyltransferase, suggests that rearrangement o f nucleosomes may be one important means by which ADR1 activates trans cription.