Polycomb repressive complexes 1 and 2 (PRC1 and PRC2) are transcriptional repressor complexes that play a fundamental role in epigenomic regulation and the cell-fate decision; these complexes are widely conserved in multicellular organisms. PRC1 is an E3 ubiquitin (ub) ligase that generates histone H2A ubiquitinated at lysine (K) 119 (H2AK119ub1), whereas PRC2 is a histone methyltransferase that specifically catalyzes tri-methylation of histone H3K27 (H3K27me3). Genome-wide analyses have confirmed that these two key epigenetic marks highly overlap across the genome and contribute to gene repression. We are now beginning to understand the molecular mechanisms that enable PRC1 and PRC2 to identify their target sites in the genome and communicate through feedback mechanisms to create Polycomb chromatin domains. Recently, it has become apparent that PRC1-induced H2AK119ub1 not only serves as a docking site for PRC2 but also affects the dynamics of the H3 tail, both of which enhance PRC2 activity, suggesting that trans-tail communication between H2A and H3 facilitates the formation of the Polycomb chromatin domain. In this review, we discuss the emerging principles that define how PRC1 and PRC2 establish the Polycomb chromatin domain and regulate gene expression in mammals.
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Cover Image
Cover Image
Gas vesicles are protein megacomplexes filled with gas to allow aquatic bacteria to control their vertical position in the water column. The cover image shows a detailed model of a complete gas vesicle. The model is deposited and made publicly available in a data repository (zenodo.org/record/6458345). Besides the striking geometry of the structure, the image also highlights the function of gas vesicles as buoyancy devices (filled with yellow gas) and the gas-permeability of the wall (with yellow gas molecules diffusing around). For more information, see the article by Huber and Jakobi (pp. 205–215) in this issue. Image provided by Arjen Jakobi.
Polycomb-mediated histone modifications and gene regulation
Shinsuke Ito, Takashi Umehara, Haruhiko Koseki; Polycomb-mediated histone modifications and gene regulation. Biochem Soc Trans 28 February 2024; 52 (1): 151–161. doi: https://doi.org/10.1042/BST20230336
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