Nucleosomal asymmetry shapes histone mark binding and promotes poising at bivalent domains.

Promoters of developmental genes in embryonic stem cells (ESCs) are marked by histone H3 lysine 4 trimethylation (H3K4me3) and H3K27me3 in an asymmetric nucleosomal conformation, with each sister histone H3 carrying only one of the two marks. These bivalent domains are thought to poise genes for timely activation upon differentiation. Here, we show that asymmetric bivalent nucleosomes recruit repressive H3K27me3 binders but fail to enrich activating H3K4me3 binders, thereby promoting a poised state.

H3.1K27M-induced misregulation of the TSK/TONSL-H3.1 pathway causes genomic instability.

The oncomutation lysine 27-to-methionine in histone H3 (H3K27M) is frequently identified in tumors of patients with diffuse midline glioma-H3K27 altered (DMG-H3K27a). H3K27M inhibits the deposition of the histone mark H3K27me3, which affects the maintenance of transcriptional programs and cell identity. Cells expressing H3K27M are also characterized by defects in genome integrity, but the mechanisms linking expression of the oncohistone to DNA damage remain mostly unknown.

The N-terminal region of DNMT3A engages the nucleosome surface to aid chromatin recruitment.

DNA methyltransferase 3A (DNMT3A) plays a critical role in establishing and maintaining DNA methylation patterns in vertebrates. Here we structurally and biochemically explore the interaction of DNMT3A1 with diverse modified nucleosomes indicative of different chromatin environments. A cryo-EM structure of the full-length DNMT3A1-DNMT3L complex with a H2AK119ub nucleosome reveals that the DNMT3A1 ubiquitin-dependent recruitment (UDR) motif interacts specifically with H2AK119ub and makes extensive contacts with the core nucleosome histone surface.

Two-factor authentication underpins the precision of the piRNA pathway.

The PIWI-interacting RNA (piRNA) pathway guides the DNA methylation of young, active transposons during germline development in male mice. piRNAs tether the PIWI protein MIWI2 (PIWIL4) to the nascent transposon transcript, resulting in DNA methylation through SPOCD1 (refs. ).