Project description:Mcm2, a subunit of the minichromosome maintenance proteins 2-7 (Mcm2-7) helicase best known for its role in DNA replication, contains a histone binding motif that facilitates the transfer of parental histones following DNA replication. Here, we show that Mcm2 is important for the differentiation of mouse embryonic stem (ES) cells. The Mcm2-2A mutation defective in histone binding shows defects in silencing of pluripotent genes and the induction of lineage-specific genes. The defects in the induction of lineage-specific genes in the mutant cells are likely, at least in part, due to reduced binding to Asf1a, a histone chaperone that binds Mcm2 and is important for nucleosome disassembly at bivalent chromatin domains containing repressive H3K27me3 and active H3K4me3 modifications during differentiation. Mcm2 localizes at transcription starting sites and the binding of Mcm2 at gene promoters is disrupted in both Mcm2-2A ES cells and neural precursor cells (NPCs). Reduced Mcm2 binding at bivalent chromatin domains in Mcm2-2A ES cells correlates with decreased chromatin accessibility at corresponding sites in NPCs. Together, our studies reveal a novel function of Mcm2 in ES cell differentiation, likely through manipulating chromatin landscapes at bivalent chromatin domains.
Project description:Mcm2, a subunit of the Mcm2-7 helicase best known for its role in DNA replication, contains a histone binding motif that facilitates the transfer of parental histone following DNA replication. Here we show that Mcm2 is important for the differentiation of mouse embryonic stem (ES) cells. Mcm2-2A mutation defective in histone binding impairs differentiation and programmatic changes in gene expression and histone modifications during differentiation. Mcm2 localizes at the transcription starting sites and the binding of Mcm2 at gene promoters is disrupted in both Mcm2-2A ES cells and neuro-precursor cells (NPCs). Reduced Mcm2 binding in Mcm2-2A ES cells correlates with decreased chromatin accessibility at bivalent chromatin domains containing repressive H3K27me3 and active H3K4me3 modifications in NPCs. Together, our studies reveal a novel function of Mcm2 in ES differentiation, likely through manipulating chromatin landscape at bivalent chromatin domains.
Project description:Mcm2, a subunit of the Mcm2-7 helicase best known for its role in DNA replication, contains a histone binding motif that facilitates the transfer of parental histone following DNA replication. Here we show that Mcm2 is important for the differentiation of mouse embryonic stem (ES) cells. Mcm2-2A mutation defective in histone binding impairs differentiation and programmatic changes in gene expression and histone modifications during differentiation. Mcm2 localizes at the transcription starting sites and the binding of Mcm2 at gene promoters is disrupted in both Mcm2-2A ES cells and neuro-precursor cells (NPCs). Reduced Mcm2 binding in Mcm2-2A ES cells correlates with decreased chromatin accessibility at bivalent chromatin domains containing repressive H3K27me3 and active H3K4me3 modifications in NPCs. Together, our studies reveal a novel function of Mcm2 in ES differentiation, likely through manipulating chromatin landscape at bivalent chromatin domains.
Project description:Although essential for epigenetic inheritance, the transfer of parental histone (H3-H4)2 tetramers that contain epigenetic modifications to replicating DNA strands is poorly understood. Here, we show that the Mcm2-Ctf4-Pol? axis facilitates the transfer of parental (H3-H4)2 tetramers to lagging-strand DNA at replication forks. Mutating the conserved histone-binding domain of the Mcm2 subunit of the CMG (Cdc45-MCM-GINS) DNA helicase, which translocates along the leading-strand template, results in a marked enrichment of parental (H3-H4)2 on leading strand, due to the impairment of the transfer of parental (H3-H4)2 to lagging strands. Similar effects are observed in Ctf4 and Pol? primase mutants that disrupt the connection of the CMG helicase to Pol? that resides on lagging-strand template. Our results support a model whereby parental (H3-H4)2 complexes displaced from nucleosomes by DNA unwinding at replication forks are transferred by the CMG-Ctf4-Pol? complex to lagging-strand DNA for nucleosome assembly at the original location.
Project description:During DNA replication, chromatin is reassembled by recycling of modified old histones and deposition of new ones. How histone dynamics integrates with DNA replication to maintain genome and epigenome information remains unclear. Here, we reveal how human MCM2, part of the replicative helicase, chaperones histones H3-H4. Our first structure shows an H3-H4 tetramer bound by two MCM2 histone-binding domains (HBDs), which hijack interaction sites used by nucleosomal DNA. Our second structure reveals MCM2 and ASF1 cochaperoning an H3-H4 dimer. Mutational analyses show that the MCM2 HBD is required for MCM2-7 histone-chaperone function and normal cell proliferation. Further, we show that MCM2 can chaperone both new and old canonical histones H3-H4 as well as H3.3 and CENPA variants. The unique histone-binding mode of MCM2 thus endows the replicative helicase with ideal properties for recycling histones genome wide during DNA replication.
Project description:Histone chaperones physically interact with histones to direct proper assembly and disassembly of nucleosomes regulating diverse nuclear processes such as DNA replication, promoter remodeling, transcription elongation, DNA damage, and histone variant exchange. Currently, the best-characterized chaperone-histone interaction is that between the ubiquitous chaperone Asf1 and a dimer of H3 and H4. Nucleosome assembly proteins (Nap proteins) represent a distinct class of histone chaperone. Using pulsed electron double resonance (PELDOR) measurements and protein crosslinking, we show that two members of this class, Nap1 and Vps75, bind histones in the tetrameric conformation also observed when they are sequestered within the nucleosome. Furthermore, H3 and H4 trapped in their tetrameric state can be used as substrates in nucleosome assembly and chaperone-mediated lysine acetylation. This alternate mode of histone interaction provides a potential means of maintaining the integrity of the histone tetramer during cycles of nucleosome reassembly.
Project description:The yeast histone chaperone Rtt106 is involved in de novo assembly of newly synthesized histones into nucleosomes during DNA replication and plays a role in regulating heterochromatin silencing and maintaining genomic integrity. The interaction of Rtt106 with H3-H4 is modulated by acetylation of H3 lysine 56 catalyzed by the lysine acetyltransferase Rtt109. Using affinity purification strategies, we demonstrate that Rtt106 interacts with (H3-H4)(2) heterotetramers in vivo. In addition, we show that Rtt106 undergoes homo-oligomerization in vivo and in vitro, and mutations in the N-terminal homodimeric domain of Rtt106 that affect formation of Rtt106 oligomers compromise the function of Rtt106 in transcriptional silencing and response to genotoxic stress and the ability of Rtt106 to bind (H3-H4)(2). These results indicate that Rtt106 deposits H3-H4 heterotetramers onto DNA and provide the first description of a H3-H4 chaperone binding to (H3-H4)(2) heterotetramers in vivo.