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Open Access Research

Proteogenomic characterization and mapping of nucleosomes decoded by Brd and HP1 proteins

Gary LeRoy1, Iouri Chepelev2, Peter A DiMaggio1, Mario A Blanco1, Barry M Zee13, Keji Zhao2 and Benjamin A Garcia1345*

Author Affiliations

1 Department of Molecular Biology, Princeton University, 415 Schultz Laboratory, Princeton NJ 08544, USA

2 Systems Biology Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA

3 Epigenetics Program, Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, 1009C Stellar-Chance Laboratories, 422 Curie Boulevard, Philadelphia, PA19104, USA

4 Department of Chemistry, Princeton University, Princeton NJ 08544, USA

5 Quantitative and Computational Biology Program, Princeton University, Princeton, NJ 08544, USA

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Genome Biology 2012, 13:R68  doi:10.1186/gb-2012-13-8-r68

Published: 16 August 2012

Abstract

Background

Histone post-translational modifications (PTMs) constitute a branch of epigenetic mechanisms that can control the expression of eukaryotic genes in a heritable manner. Recent studies have identified several PTM-binding proteins containing diverse specialized domains whose recognition of specific PTM sites leads to gene activation or repression. Here, we present a high-throughput proteogenomic platform designed to characterize the nucleosomal make-up of chromatin enriched with a set of histone PTM binding proteins known as histone PTM readers. We support our findings with gene expression data correlating to PTM distribution.

Results

We isolated human mononucleosomes bound by the bromodomain-containing proteins Brd2, Brd3 and Brd4, and by the chromodomain-containing heterochromatin proteins HP1β and HP1α. Histone PTMs were quantified by mass spectrometry (ChIP-qMS), and their associated DNAs were mapped using deep sequencing. Our results reveal that Brd- and HP1-bound nucleosomes are enriched in histone PTMs consistent with actively transcribed euchromatin and silent heterochromatin, respectively. Data collected using RNA-Seq show that Brd-bound sites correlate with highly expressed genes. In particular, Brd3 and Brd4 are most enriched on nucleosomes located within HOX gene clusters, whose expression is reduced upon Brd4 depletion by short hairpin RNA.

Conclusions

Proteogenomic mapping of histone PTM readers, alongside the characterization of their local chromatin environments and transcriptional information, should prove useful for determining how histone PTMs are bound by these readers and how they contribute to distinct transcriptional states.