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Nature. 2017 Jan 12;541(7636):237-241. doi: 10.1038/nature20781. Epub 2016 Dec 26.

Variable chromatin structure revealed by in situ spatially correlated DNA cleavage mapping.

Author information

1
Department of Genetics, Stanford University School of Medicine, Stanford, California 94305, USA.
2
Biophysics Program, Stanford University, Stanford, California 94305, USA.
3
Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, USA.
4
Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, California 94305, USA.
5
Department of Applied Physics, Stanford University School of Medicine, Stanford, California 94305, USA.

Abstract

Chromatin structure at the length scale encompassing local nucleosome-nucleosome interactions is thought to play a crucial role in regulating transcription and access to DNA. However, this secondary structure of chromatin remains poorly understood compared with the primary structure of single nucleosomes or the tertiary structure of long-range looping interactions. Here we report the first genome-wide map of chromatin conformation in human cells at the 1-3 nucleosome (50-500 bp) scale, obtained using ionizing radiation-induced spatially correlated cleavage of DNA with sequencing (RICC-seq) to identify DNA-DNA contacts that are spatially proximal. Unbiased analysis of RICC-seq signal reveals regional enrichment of DNA fragments characteristic of alternating rather than adjacent nucleosome interactions in tri-nucleosome units, particularly in H3K9me3-marked heterochromatin. We infer differences in the likelihood of nucleosome-nucleosome contacts among open chromatin, H3K27me3-marked, and H3K9me3-marked repressed chromatin regions. After calibrating RICC-seq signal to three-dimensional distances, we show that compact two-start helical fibre structures with stacked alternating nucleosomes are consistent with RICC-seq fragmentation patterns from H3K9me3-marked chromatin, while non-compact structures and solenoid structures are consistent with open chromatin. Our data support a model of chromatin architecture in intact interphase nuclei consistent with variable longitudinal compaction of two-start helical fibres.

PMID:
28024297
PMCID:
PMC5526328
DOI:
10.1038/nature20781
[Indexed for MEDLINE]
Free PMC Article

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