Transcription factor binding can displace nucleosomes. The promoter region of GTR1 is known to contain high-affinity binding sites of Pho4 and Nrg1, as well as several of Pho2. (A) An occupancy profile including only nucleosomes depicts five to six reasonably well-positioned nucleosomes beginning atop the start codon of YML122C. (B) Addition of Pho4, Pho2, and Nrg1 to the model results in the displacement of several of the previously bound nucleosomes, and the reduction of binding frequency of those remaining, to various extents. Additionally, a well-positioned nucleosome is established near the 3′-end of YML122C. The strong TF binding in this region precludes nucleosome repositioning upstream or downstream along the sequence; the strongly bound TFs displace some nucleosomes and hem in the remaining others, resulting in their well-defined positions.
