title: Nucleosome binding by the bromodomain and PHD finger of the transcriptional cofactor p300.
abstract: The PHD finger and the bromodomain are small protein domains that occur in many proteins associated with phenomena related to chromatin. The bromodomain has been shown to bind acetylated lysine residues on histone tails. Lysine acetylation is one of several histone modifications that have been proposed to form the basis for a mechanism for recording epigenetically stable marks in chromatin, known as the histone code. The bromodomain is therefore thought to read a part of the histone code. Since PHD fingers often occur in proteins next to bromodomains, we have tested the hypothesis that the PHD finger can also interact with nucleosomes. Using two different in vitro assays, we found that the bromodomain/PHD finger region of the transcriptional cofactor p300 can bind to nucleosomes that have a high degree of histone acetylation. In a nucleosome retention assay, both domains were required for binding. Replacement of the p300 PHD finger with other PHD fingers resulted in loss of nucleosome binding. In an electrophoretic mobility shift assay, each domain alone showed, however, nucleosome-binding activity. The binding of the isolated PHD finger to nucleosomes was independent of the histone acetylation levels. Our data are consistent with a model where the two domains cooperate in nucleosome binding. In this model, both the bromodomain and the PHD finger contact the nucleosome while simultaneously interacting with each other.
authors.affiliation: Department of Molecular Biology, University of Bergen, HIB, Thormöhlensgt 55, N-5020 Bergen, Norway.
authors.forename: Anja
authors.initials: A
authors.lastname: Ragvin
authors.forename: Håvard
authors.initials: H
authors.lastname: Valvatne
authors.forename: Sigrid
authors.initials: S
authors.lastname: Erdal
authors.forename: Vibeke
authors.initials: V
authors.lastname: Arskog
authors.forename: Katharina R
authors.initials: KR
authors.lastname: Tufteland
authors.forename: Kamilla
authors.initials: K
authors.lastname: Breen
authors.forename: Anne M
authors.initials: AM
authors.lastname: ØYan
authors.forename: Anton
authors.initials: A
authors.lastname: Eberharter
authors.forename: Toby J
authors.initials: TJ
authors.lastname: Gibson
authors.forename: Peter B
authors.initials: PB
authors.lastname: Becker
authors.forename: Rein
authors.initials: R
authors.lastname: Aasland
mesh_terms: D006657:Histones / Q000378:metabolism; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism*; D009707:Nucleosomes / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D015534:Trans-Activators / Q000378:metabolism*
chemical_list: D006657:Histones; D009687:Nuclear Proteins; D009707:Nucleosomes; D015534:Trans-Activators