Tatarakis et al. study how H3K9me3 heterochromatin is formed and inherited in mammalian cells. Using a synthetic heterochromatin assembly system and genetic screens, they uncover requirements for init...

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CDK7 kinase activity is found to control RNAPII transcription through a cohort of TFs that drive cell cycle and proliferation.

During transcription, RNA polymerase II traverses through chromatin, and posttranslational modifications including histone methylations mark regions of active transcription. Histone protein H3 lysine ...

Mohamed et al. report the cryoelectron microscopy structure of human AGO2 with fully paired guide RNA. Their analysis reveals the structural basis for the slicing activity that drives RNAi, showing that the slicing-competent conformation is achieved by domain movements and RNA-protein contacts distinct from those of conformational intermediates and prokaryotic homologs.

Reversible modification of the histone H3 N-terminal tail is critical in regulating the chromatin structure, gene expression, and cell states, while its dysregulation contributes to disease pathogenesis. Understanding the crosstalk between H3 tail modifications in nucleosomes constitutes a central challenge in epigenetics. Here, we describe an engineered sortase transpeptidase, cW11, that displays highly favorable properties for introducing scarless H3 tails onto nucleosomes. This approach significantly accelerates the production of both symmetrically and asymmetrically modified nucleosomes. We demonstrate the utility of asymmetrically modified nucleosomes produced in this way in dissecting the impact of multiple modifications on eraser enzyme processing and molecular recognition by a reader protein. Moreover, we show that cW11 sortase is very effective at cutting and tagging histone H3 tails from endogenous histones, facilitating multiplex “cut-and-paste” middle-down proteomics with tandem mass tags. This cut-and-paste proteomics approach permits the quantitative analysis of histone H3 modification crosstalk after treatment with different histone deacetylase inhibitors. We propose that these chemoenzymatic tail isolation and modification strategies made possible with cW11 sortase will broadly power epigenetic discovery and therapeutic development.