title: Replication-independent core histone dynamics at transcriptionally active loci in vivo.
abstract: We used a novel labeling technique in the naturally synchronous organism Physarum polycephalum to examine the fate of core histones in G2 phase. We find rapid exchange of H2A/H2B dimers with free pools that is greatly diminished by treatment of the cells with alpha-amanitin. This exchange is enhanced in pol II-coding sequences compared with extragenic regions or inactive loci. In contrast, H3/H4 tetramers exhibit far lower levels of exchange in the pol II-transcribed genes tested, suggesting that tetramer exchange occurs via a distinct mechanism. However, we find that transcribed regions of the ribosomal RNA gene loci exhibit rapid exchange of H3/H4 tetramers. Thus, our data show that the majority of the pol II transcription-dependent histone exchange is due to elongation in vivo rather than promoter remodeling or other pol II-dependent alterations in promoter structure and, in contrast to pol I, pol II transcription through nucleosomes in vivo causes facile exchange of both H2A/H2B dimers while allowing conservation of epigenetic "marks" and other post-translational modifications on H3 and H4.
authors.affiliation: Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York 14642, USA.
authors.forename: Christophe
authors.initials: C
authors.lastname: Thiriet
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Hayes
mesh_terms: D000546:Amanitins; D000818:Animals; D002843:Chromatin / Q000737:chemistry*; D004257:DNA Polymerase II / Q000235:genetics; D019281:Dimerization; D016195:G2 Phase / Q000502:physiology*; D006657:Histones / Q000378:metabolism* / Q000502:physiology; D047468:Immunoprecipitation; D008856:Microscopy, Fluorescence; D016839:Physarum polycephalum; D012335:RNA, Ribosomal / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics / Q000502:physiology*; D014981:Xenopus
chemical_list: D000546:Amanitins; D002843:Chromatin; D006657:Histones; D012335:RNA, Ribosomal; D004257:DNA Polymerase II