Rockefeller University's Ronen Sadeh and C. David Allis discuss in the current issue of Cell the relevance of recent studies that have mapped nucelosomes across the yeast and human genomes. Sadeh and Allis say that data from these studies suggest two models of nucleosome organization: "Chromatin remodelers position nucleosomes around transcriptional start sites in yeast, and a few locked nucleosomes may serve as barriers from which nucleosome arrays emanate in human genomes."