Gcn4 Occupancy Of Open Reading Frame Regions Results In The Recruitment Of Chromatin-Modifying Complexes But Not The Mediator Complex

Eukaryotic transcriptional activators usually recognize short DNA motifs, which are not only located within promoter regions, but also scattered throughout the genome. Assuming that the function of activators at non-promoter regions is wasteful and perhaps harmful, one can ask whether such binding is somehow prevented or if transcription is blocked at a downstream step. Here, we show that the yeast transcriptional activator Gcn4 is associated in vivo with several non-promoter euchromatic sites. This association results in the recruitment of the SAGA (Spt3/Ada/Gcn5/ acetyltransferase) complex and the consequent activity of the Gcn5 histone acetyltransferase. The functional recruitment of the Swi/Snf nucleosome-remodelling complex was also evident at sites located in positioned nucleosomes. We show that this assemblage of coactivator complexes is not productive because of the absence of core promoter elements, other than the TATA box, that are required for stable mediator recruitment.