Condensed mitotic chromatin is accessible to transcription factors and chromatin structural proteins.
During mitosis, chromosomes are highly condensed and transcription is silenced globally. One explanation for transcriptional repression is the reduced accessibility of transcription factors. To directly test this hypothesis and to investigate the dynamics of mitotic chromatin, we evaluate the exchange kinetics of several RNA polymerase I transcription factors and nucleosome components on mitotic chromatin in living cells. We demonstrate that these factors rapidly exchange on and off ribosomal DNA clusters and that the kinetics of exchange varies at different phases of mitosis. In addition, the nucleosome component H1c-GFP also shows phase-specific exchange rates with mitotic chromatin. Furthermore, core histone components exchange at detectable levels that are elevated during anaphase and telophase, temporally correlating with H3-K9 acetylation and recruitment of RNA polymerase II before the onset of bulk RNA synthesis at mitotic exit. Our findings indicate that mitotic chromosomes in general and ribosomal genes in particular, although highly condensed, are accessible to transcription factors and chromatin proteins. The phase-specific exchanges of nucleosome components during late mitotic phases are consistent with an emerging model of replication independent core histone replacement.
Chen
Danyang
D
Department of Cell and Molecular Biology, The Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.
Dundr
Miroslav
M
Wang
Chen
C
Leung
Anthony
A
Lamond
Angus
A
Misteli
Tom
T
Huang
Sui
S
D000107:Acetylation; D002843:Chromatin / Q000378:metabolism*; D004275:DNA, Ribosomal / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D036681:Fluorescence Recovery After Photobleaching; D006367:HeLa Cells; D006657:Histones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006801:Humans; D046911:Macromolecular Substances; D008938:Mitosis / Q000502:physiology*; D016296:Mutagenesis; D009697:Nucleolus Organizer Region / Q000378:metabolism; D009707:Nucleosomes / Q000737:chemistry / Q000378:metabolism*; D035463:Pol1 Transcription Initiation Complex Proteins / Q000235:genetics / Q000378:metabolism; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D012318:RNA Polymerase I / Q000235:genetics / Q000378:metabolism; D012319:RNA Polymerase II / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic
D002843:Chromatin; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D006657:Histones; D046911:Macromolecular Substances; D009707:Nucleosomes; D035463:Pol1 Transcription Initiation Complex Proteins; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C063844:transcription factor UBF; D012319:RNA Polymerase II; D012318:RNA Polymerase I