Project description:The hexameric DNA helicase MCM (Mcm2-7) is a central regulatory target in eukaryotic replication. Chromatin-bound MCM is kept inactive during G1 phase and subsequently activated in S phase to initiate replication. During this transition, the only known chemical change on the Mcm2-7 proteins is the gain of multi-site phosphorylation that promotes recruitment of co-factors. As replication initiation is tied intimately to multiple biological cues, additional changes on these proteins can provide a second regulatory point. Here we describe a new MCM modification cycle mediated by SUMO that enables a negative regulation of replication initiation. We show that all MCM subunits undergo sumoylation upon loading at origins in G1 phase prior to MCM phosphorylation. Then bulk MCM sumoylation is lost as MCM phosphorylation rises. The pattern of MCM sumoylation suggests a negative role in replication. Indeed, increasing MCM sumoylation delays genome-wide replication initiation. Mechanistically, this is partly due to enhancing the recruitment of a conserved phosphatase that delays MCM phosphorylation and activation. By revealing a new MCM modification cycle and its role in replication, our findings suggest a new model, in which MCM sumoylation counterbalances kinase-based regulation to ensure accurate control of replication initiation.
Project description:The minichromosome maintenance complex (MCM) DNA helicase is an important replicative factor during DNA replication. The proper chromatin loading of MCM is a key step to ensure replication initiation during G1/S phase. Because replication initiation is regulated by multiple biological cues, additional changes to MCM may provide deeper understanding towards this event. Here, we uncover that the histidine methyltransferase SETD3 promotes DNA replication in an enzymatic activity dependent manner. Nascent-strand sequencing (NS-seq) shows that SETD3 regulates replication initiation, as depletion of SETD3 attenuates early replication origins firing. Mechanistically, biochemical experiments reveal that SETD3 binds MCM mainly during G1/S phase, which is required for CDT1-mediated chromatin loading of MCM. The MCM loading relies on the histidine-459 methylation (H459me) on MCM7 that is catalyzed by SETD3. Impairment of H459 methylation attenuates DNA synthesis and chromatin loading of MCM. Furthermore, we show that CDK2 phosphorylates SETD3 at Serine-21 during the G1/S phase, which is required for DNA replication and cell cycle progression. These findings demonstrate a novel mechanism by which SETD3 methylates MCM to regulate replication initiation.
Project description:There are approximately 500 known origins of replication in the yeast genome, and the process by which DNA replication initiates at these locations is well understood. In particular, these sites are made competent to initiate replication by loading of the Mcm replicative helicase prior to the start of S phase; thus, "a site to which MCM is bound in G1" might be considered to provide an operational definition of a replication origin. By fusing a subunit of Mcm to micrococcal nuclease, a technique referred to as "Chromatin Endogenous Cleavage", we previously showed that known origins are typically bound by a single Mcm double hexamer, loaded adjacent to the ARS consensus sequence (ACS). Here we extend this analysis from known origins to the entire genome, identifying candidate Mcm binding sites whose signal intensity varies over at least 3 orders of magnitude. Published data quantifying the production of ssDNA during S phase showed clear evidence of replication initiation among the most abundant 1600 of these sites, with replication activity decreasing in concert with Mcm abundance and disappearing at the limit of detection of ssDNA. Three other hallmarks of replication origins were apparent among the most abundant 5,500 sites. Specifically, these sites (1) appeared in intergenic nucleosome-free regions that were flanked on one or both sides by well-positioned nucleosomes; (2) were flanked by ACSs; and (3) exhibited a pattern of GC skew characteristic of replication initiation. Furthermore, the high resolution of this technique allowed us to demonstrate a strong bias for detecting Mcm double-hexamers downstream rather than upstream of the ACS, which is consistent with the directionality of Mcm loading by Orc that has been observed in vitro. We conclude that DNA replication origins are at least 3-fold more abundant than previously assumed, and we suggest that replication may occasionally initiate in essentially every intergenic region. These results shed light on recent reports that as many as 15% of replication events initiate outside of known origins, and this broader distribution of replication origins suggest that S phase in yeast may be less distinct from that in humans than is widely assumed.
Project description:This project is the complete interactome of the Minichromosome Maintenance (MCM) complex by using AP-MS and BioID approaches for all the different MCM proteins. Overall, our analysis identified unique and shared interaction partners and proteins enriched for distinct biological processes including DNA replication, DNA repair and cell cycle regulation. Furthermore, we mapped the changes in protein interactions of the MCM complex in response to DNA damage, identifying a new role for this complex in DNA repair. In summary, we demonstrate the complementarity of these approaches for the characterization of protein interactions within the MCM complex.
Project description:Assembly of the DNA helicase known as CMG (CDC45-MCM-GINS) is the key regulated step during DNA replication initiation in eukaryotes. Using the Caenorhabditis elegans embryo as a model system, we identify a new CMG assembly factor called DNSN-1, which associates with the BRCT-domain protein MUS-101. We show that DNSN-1 is required to recruit the GINS complex to chromatin and find that DNSN-1 positions GINS on the MCM-2-7 helicase motor, by direct binding of DNSN-1 to GINS and MCM-3, on interfaces that are important for initiation and essential for viability.
Project description:We develop a high-throughput nucleoside analog incorporation sequencing assay and identify thousands of early replication initiation zones (ERIZs) in both mouse and human cells. The identified ERIZs fall in open chromatin compartments while are mutually exclusive with transcription elongation and occupy mainly non-transcribed regions adjacent to transcribed regions. Furthermore, we reveal that RNA polymerase II actively redistributes the chromatin-encircled mini-chromosome maintenance (MCM) complex but not the origin-recognition complex (ORC) to actively restrict early DNA replication initiation outside of transcribed regions. The coupling of RNA polymerase II and MCM is further validated by detected MCM accumulation and DNA replication initiation after RNA polymerase II stalling via anchoring nuclease-dead Cas9 at the transcribed genes. Importantly, we also find that the orchestration of DNA replication initiation by transcription can efficiently prevent gross DNA damage.
Project description:This project is the complete interactome of the Minichromosome Maintenance (MCM) complex by using AP-MS and BioID approaches for all the different MCM proteins. Overall, our analysis identified unique and shared interaction partners and proteins enriched for distinct biological processes including DNA replication, DNA repair and cell cycle regulation. Furthermore, we mapped the changes in protein interactions of the MCM complex in response to DNA damage, identifying a new role for this complex in DNA repair. In summary, we demonstrate the complementarity of these approaches for the characterization of protein interactions within the MCM complex.