Global patterns of nucleosome positioning in wild-type and deletion mutant strains. (a) Heatmaps of nucleosome scores for the wild-type and Δisw1 S. cerevisiae strains. Genes were divided into four clusters by k-means clustering. (b) Average pattern of nucleosome positioning for all yeast genes in the wild-type (WT) and three mutant strains, shown as percentage of reads mapped to different positions relative to transcription start sites (TSSs). Nucleosome numbering is shown at the top . The same analysis was performed for S. cerevisiae (top), S. paradoxus (middle) and their inter-specific hybrid (bottom), using the TSS positions from S. cerevisiae .