ORC and nucleosome binding at ARS1. The origin recognition complex (ORC) and chromatin play strong roles in the initiation of DNA replication. ARS1, an origin of replication in yeast, has a well-characterized DNA occupancy structure including binding by ORC, nucleosomes, and the transcription factor Abf1. This structure is observed to change in the absence of ORC binding, as can be seen in Figure 2A of Lipford and Bell (2001). The Abf1 binding site annotation is taken from Marahrens and Stillman (1992). The ORC binding site and sequence preferences are derived from Xu et al. (2006). (A) The wild-type occupancy profile recapitulates the strong binding of nucleosomes adjacent to the Abf1 and ORC binding sites, as well as the nucleosome-free region between them. (B) Without ORC present, the occupancy profile depicts a shifted nucleosome over the top of the ORC binding site, as is the case in the experimental observation of Lipford and Bell (2001).
