title: Identification of a rapidly formed nonnucleosomal histone-DNA intermediate that is converted into chromatin by ACF.
abstract: Chromatin assembly involves the combined action of histone chaperones and ATP-dependent motor proteins. Here, we investigate the mechanism of nucleosome assembly with a purified chromatin assembly system containing the histone chaperone NAP1 and the ATP-dependent motor protein ACF. These studies revealed the rapid formation of a stable nonnucleosomal histone-DNA intermediate that is converted into canonical nucleosomes by ACF. The histone-DNA intermediate does not supercoil DNA like a canonical nucleosome, but has a nucleosome-like appearance by atomic force microscopy. This intermediate contains all four core histones, lacks NAP1, and is formed by the initial deposition of histones H3-H4. Conversion of the intermediate into histone H1-containing chromatin results in increased resistance to micrococcal nuclease digestion. These findings suggest that the histone-DNA intermediate corresponds to nascent nucleosome-like structures, such as those observed at DNA replication forks. Related complexes might be formed during other chromatin-directed processes such as transcription, DNA repair, and histone exchange.
authors.affiliation: Section of Molecular Biology, University of California, San Diego, La Jolla, CA 92093-0347, USA.
authors.forename: Sharon E
authors.initials: SE
authors.lastname: Torigoe
authors.forename: Debra L
authors.initials: DL
authors.lastname: Urwin
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Ishii
authors.forename: Douglas E
authors.initials: DE
authors.lastname: Smith
authors.forename: James T
authors.initials: JT
authors.lastname: Kadonaga
mesh_terms: D002843:Chromatin / Q000378:metabolism*; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D056488:Histone Chaperones / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D006657:Histones / Q000737:chemistry / Q000378:metabolism*; D020409:Molecular Motor Proteins / Q000378:metabolism / Q000502:physiology*; D009707:Nucleosomes / Q000378:metabolism*
chemical_list: D002843:Chromatin; D056488:Histone Chaperones; D006657:Histones; D020409:Molecular Motor Proteins; D009707:Nucleosomes; D004247:DNA