From Beads on a String to the Pearls of Regulation: the Structure and Dynamics of Chromatin Nucleosome recognition and spacing by chromatin remodelling factor ISW1a

Abstract Nucleosomes are actively positioned along DNA by ATP-dependent, chromatin remodelling factors. A structural model for the ISW1a chromatin remodelling factor from Saccharomyces cerevisiae in complex with a dinucleosome substrate was constructed from the X-ray structures of ISW1a ( ATPase) with and without DNA bound, two different cryo-EM (cryo-electron microscopy) structures of ISW1a ( ATPase) bound to a nucleosome, and site-directed photo-cross-linking analyses in solution. The X-ray structure of ISW1a ( ATPase) with DNA bound suggests that DNA sequence may be involved in nucleosome recognition and thereby specificity of promoter interaction. The model suggests how the highly ordered nucleosome arrays observed by mapping nucleosomes in genes and their promoter regions could be generated by a chromatin remodelling factor