Gene expression profile of Tra1 dependent genes

Promoter-specific transcriptional activators (activators) stimulate transcription through direct interactions with one or more components of the transcription machinery, termed the target. Previous studies have provided evidence that the Tra1 subunit of the yeast SAGA (Spt-Ada-Gcn5-acetyltransferase) complex is the target of the yeast activator Gal4. However, several other general transcription factors, in particular the mediator complex, have also been implicated as Gal4 targets. To investigate the essentiality of Tra1 as a target of Gal4, here we derive Tra1 mutants that are selectively defective for interaction with Gal4 in vivo (Gal4 Interaction Defective (GID) mutants). In contrast to wild-type Tra1, Tra1 GID mutants are not recruited by Gal4 to the promoter and cannot support Gal4-directed transcription activation, demonstrating that the Gal4Tra1 interaction is required for Gal4 function. In yeast strains expressing a Tra1 GID mutant, Gal4 promoter binding is unexpectedly also diminished indicating that Gal4 and Tra1 bind cooperatively. Consistent with cooperative binding, we demonstrate that the interaction between Gal4 and Tra1 occurs predominantly on the promoter and not off DNA. Finally, we show that although Tra1 is also targeted by other activators, these interaction are unaffected by GID mutations, revealing an unanticipated specificity of the Gal4-Tra1 interaction.

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Lin L, Chamberlain L, Zhu LJ, Green MR