Figure 3.

Nucleosome spacing and nucleosome phasing. (A) Nucleosomes can be regularly spaced but not phased on the same stretch of DNA. They are the same distance apart but in different positions in different cells. (B) Nucleosomes are regularly spaced and perfectly phased on the same stretch of DNA. They are the same distance apart and in the same positions in every cell. (C) Model for the origin of phasing. A putative “barrier complex” is formed at a specific sequence such as a promoter (blue box), preventing nucleosome formation on the DNA that it occupies and forcing nucleosomes to form on either side. If they are regularly spaced, phasing will result. (D) Model for phasing which takes into account observed variation in nucleosome positions and linker length (spacing).