Human SIRT1 regulates DNA binding and stability of the Mcm10 DNA replication factor via deacetylation

Unwinding Helicase MCM Functionality for Diagnosis and Therapeutics of Replication Abnormalities Associated with Cancer: A Review

The minichromosome maintenance (MCM) protein is a component of an active helicase that is essential for the initiation of DNA replication. Dysregulation of MCM functions contribute to abnormal cell proliferation and genomic instability. The interactions of MCM with cellular factors, including Cdc45 and GINS, determine the formation of active helicase and functioning of helicase. The functioning of MCM determines the fate of DNA replication and, thus, genomic integrity. This complex is upregulated in precancerous cells and can act as an important tool for diagnostic applications. The MCM protein complex can be an important broad-spectrum therapeutic target in various cancers. Investigations have supported the potential and applications of MCM in cancer diagnosis and its therapeutics. In this article, we discuss the physiological roles of MCM and its associated factors in DNA replication and cancer pathogenesis.

DNA replication: Mechanisms and therapeutic interventions for diseases

Accurate and integral cellular DNA replication is modulated by multiple replication-associated proteins, which is fundamental to preserve genome stability. Furthermore, replication proteins cooperate with multiple DNA damage factors to deal with replication stress through mechanisms beyond their role in replication. Cancer cells with chronic replication stress exhibit aberrant DNA replication and DNA damage response, providing an exploitable therapeutic target in tumors. Numerous evidence has indicated that posttranslational modifications (PTMs) of replication proteins present distinct functions in DNA replication and respond to replication stress. In addition, abundant replication proteins are involved in tumorigenesis and development, which act as diagnostic and prognostic biomarkers in some tumors, implying these proteins act as therapeutic targets in clinical. Replication-target cancer therapy emerges as the times require. In this context, we outline the current investigation of the DNA replication mechanism, and simultaneously enumerate the aberrant expression of replication proteins as hallmark for various diseases, revealing their therapeutic potential for target therapy. Meanwhile, we also discuss current observations that the novel PTM of replication proteins in response to replication stress, which seems to be a promising strategy to eliminate diseases.

Resveratrol regulates Hsp60 in HEK 293T cells during activation of SIRT1 revealed by nascent protein labeling strategy

Background

Resveratrol, a well-known natural compound and nutrient, activates the deacetylation ability of SIRT1, demonstrating p53-dependent apoptosis functions in many diseases. However, the nascent proteomic fluctuation caused by resveratrol is still unclear.

Objective

In this study, we investigated the effect of resveratrol on the nascent proteome and transcriptome initiated by SIRT1 activation, and we explored the mechanism of resveratrol in HEK 293T cells.

Methods

Bioorthogonal noncanonical amino acid tagging (BONCAT) is a method used to metabolically label nascent proteins. In this strategy, L-azidohomoalanine (AHA) was used to replace methionine (Met) under different conditions. Taking advantage of the click reaction between AHA and terminal alkyne- and disulfide-functionalized agarose resin (TAD resin), we were able to efficiently separate stimulation responsive proteins from the pre-existing proteome. Resveratrol responsive proteins were identified by Liquid Chromatograph-Mass Spectrometer/Mass Spectrometer (LC-MS/MS). Furthermore, changes in mRNA levels were analyzed by transcriptome sequencing.

Results

Integrational analysis revealed a resveratrol response in HEK 293T cells and showed that Hsp60 was downregulated at both the nascent protein and mRNA levels. Knockdown of SIRT1 and Hsp60 provides evidence that resveratrol downregulated Hsp60 through SIRT1 and that Hsp60 decreased p53 through the Akt pathway.

Conclusions

This study revealed dynamic changes in the nascent proteome and transcriptome in response to resveratrol in HEK 293T cells and demonstrated that resveratrol downregulates Hsp60 by activating SIRT1, which may be a possible mechanism by which resveratrol prevents p53-dependent apoptosis by regulating Hsp60.

Preventing excess replication origin activation to ensure genome stability

Cells activate distinctive regulatory pathways that prevent excessive initiation of DNA replication to achieve timely and accurate genome duplication. Excess DNA synthesis is constrained by protein-DNA interactions that inhibit initiation at dormant origins. In parallel, specific modifications of pre-replication complexes prohibit post-replicative origin relicensing. Replication stress ensues when the controls that prevent excess replication are missing in cancer cells, which often harbor extrachromosomal DNA that can be further amplified by recombination-mediated processes to generate chromosomal translocations. The genomic instability that accompanies excess replication origin activation can provide a promising target for therapeutic intervention. Here we review molecular pathways that modulate replication origin dormancy, prevent excess origin activation, and detect, encapsulate, and eliminate persistent excess DNA.

BI-2536 Promotes Neuroblastoma Cell Death via Minichromosome Maintenance Complex Components 2 and 10

DNA replication is initiated with the recognition of the starting point of multiple replication forks by the origin recognition complex and activation of the minichromosome maintenance complex 10 (MCM10). Subsequently, DNA helicase, consisting of the MCM protein subunits MCM2-7, unwinds double-stranded DNA and DNA synthesis begins. In previous studies, replication factors have been used as clinical targets in cancer therapy. The results showed that MCM2 could be a proliferation marker for numerous types of malignant cancer. We analyzed samples obtained from patients with neuroblastoma, revealing that higher levels of MCM2 and MCM10 mRNA were associated with poor survival rate. Furthermore, we combined the results of the perturbation-induced reversal effects on the expression levels of MCM2 and MCM10 and the sensitivity correlation between perturbations and MCM2 and MCM10 from the Cancer Therapeutics Response Portal database. Small molecule BI-2536, a polo-like kinase 1 (PLK-1) inhibitor, is a candidate for the inhibition of MCM2 and MCM10 expression. To test this hypothesis, we treated neuroblastoma cells with BI-2536. The results showed that the drug decreased cell viability and reduced the expression levels of MCM2 and MCM10. Functional analysis further revealed enrichments of gene sets involved in mitochondria, cell cycle, and DNA replication for BI-2536-perturbed transcriptome. We used cellular assays to demonstrate that BI-2536 promoted mitochondria fusion, G2/M arrest, and apoptosis. In summary, our findings provide a new strategy for neuroblastoma therapy with BI-2536.

Epigenetic enzymes: A role in aging and prospects for pharmacological targeting

The development of interventions aimed at improving healthspan is one of the priority tasks for the academic and public health authorities. It is also the main objective of a novel branch in biogerontological research, geroscience. According to the geroscience concept, targeting aging is an effective way to combat age-related disorders. Since aging is an exceptionally complex process, system-oriented integrated approaches seem most appropriate for such an interventional strategy. Given the high plasticity and adaptability of the epigenome, epigenome-targeted interventions appear highly promising in geroscience research. Pharmaceuticals targeted at mechanisms involved in epigenetic control of gene activity are actively developed and implemented to prevent and treat various aging-related conditions such as cardiometabolic, neurodegenerative, inflammatory disorders, and cancer. In this review, we describe the roles of epigenetic mechanisms in aging; characterize enzymes contributing to the regulation of epigenetic processes; particularly focus on epigenetic drugs, such as inhibitors of DNA methyltransferases and histone deacetylases that may potentially affect aging-associated diseases and longevity; and discuss possible caveats associated with the use of epigenetic drugs.

Understanding the Function of Mammalian Sirtuins and Protein Lysine Acylation

Protein lysine acetylation is an important posttranslational modification that regulates numerous biological processes. Targeting lysine acetylation regulatory factors, such as acetyltransferases, deacetylases, and acetyl-lysine recognition domains, has been shown to have potential for treating human diseases, including cancer and neurological diseases. Over the past decade, many other acyl-lysine modifications, such as succinylation, crotonylation, and long-chain fatty acylation, have also been investigated and shown to have interesting biological functions. Here, we provide an overview of the functions of different acyl-lysine modifications in mammals. We focus on lysine acetylation as it is well characterized, and principles learned from acetylation are useful for understanding the functions of other lysine acylations. We pay special attention to the sirtuins, given that the study of sirtuins has provided a great deal of information about the functions of lysine acylation. We emphasize the regulation of sirtuins to illustrate that their regulation enables cells to respond to various signals and stresses.

Minichromosome maintenance protein 10 as a marker for proliferation and prognosis in lung cancer

DNA replication is a vital process in cell division where anomalies can lead to tumorigenesis. Minichromosome maintenance complex component 10 (MCM10) plays a crucial role in this process. However, the role of MCM10 in lung cancer pathogenesis remains to be elucidated. In current study, using the publicly available lung cancer Gene Expression Omnibus (GEO) datasets, and Oncomine and the Cancer Genome Atlas databases, an increased expression of MCM10 was found in lung cancer tissues compared to normal lung tissues. The high expression of MCM10 was subsequently validated in clinical specimens by reverse transcription‑quantitative PCR and immunohistochemistry. Analysis of the GEO datasets revealed that the high MCM10 expression was significantly associated with early and late recurrence, pathological stage and worse overall survival (OS). Cox's proportional hazards regression analyses revealed that MCM10 expression was an independent risk factor for poor OS and worse recurrence‑free survival both in univariate and multivariate analysis. Furthermore, the increased expression of MCM10 was enriched in cell cycle‑related processes, while in vitro transfection with small interfering RNA targeting MCM10 significantly suppressed cell viability, clone formation and induced G1 phase arrest in A549 and H661 cell lines by regulating the expression of cyclin D1 (CCND1). In addition, the current results indicated a combined effect of MCM10‑CCND1 in predicting the prognosis of lung cancer patients. Altogether, the present study provided a novel potential molecular mechanism of lung cancer progression and may aid in development of novel treatment strategies.

Extra View: Sirt1 Acts As A Gatekeeper Of Replication Initiation To Preserve Genomic Stability

Since the discovery of a yeast gene silencing modifier (Silent Information Modifier 2, SIR2) and its role in maintaining genomic stability more than two decades ago, SIR2 homologs (sirtuins) were identified in diverse species. Sirtuins are protein deacetylases that play diverse roles in proper cellular metabolism including cell cycle progression and maintenance of genomic stability. In yeast, SIR2 interacts with replication origins and protein complexes that affect both replication origin usage and gene silencing. In metazoans, the largest SIR2 homolog, SIRT1, is implicated in epigenetic modifications, circadian signaling, DNA recombination and DNA repair. Until recently, very few studies investigated the role of mammalian SIRT1 in modulating DNA replication. We discuss a newly characterized interaction between human SIRT1 and the DNA replication machinery, reviewing data from recent studies that have investigated how complex signaling pathways that involve SIRT1 affect cellular growth regulatory circuits.

Post-Translational Modifications of the Mini-Chromosome Maintenance Proteins in DNA Replication

The eukaryotic mini-chromosome maintenance (MCM) complex, composed of MCM proteins 2-7, is the core component of the replisome that acts as the DNA replicative helicase to unwind duplex DNA and initiate DNA replication. MCM10 tightly binds the cell division control protein 45 homolog (CDC45)/MCM2-7/ DNA replication complex Go-Ichi-Ni-San (GINS) (CMG) complex that stimulates CMG helicase activity. The MCM8-MCM9 complex may have a non-essential role in activating the pre-replicative complex in the gap 1 (G1) phase by recruiting cell division cycle 6 (CDC6) to the origin recognition complex (ORC). Each MCM subunit has a distinct function achieved by differential post-translational modifications (PTMs) in both DNA replication process and response to replication stress. Such PTMs include phosphorylation, ubiquitination, small ubiquitin-like modifier (SUMO)ylation, O-N-acetyl-D-glucosamine (GlcNAc)ylation, and acetylation. These PTMs have an important role in controlling replication progress and genome stability. Because MCM proteins are associated with various human diseases, they are regarded as potential targets for therapeutic development. In this review, we summarize the different PTMs of the MCM proteins, their involvement in DNA replication and disease development, and the potential therapeutic implications.

Werner Helicase Control of Human Papillomavirus 16 E1-E2 DNA Replication Is Regulated by SIRT1 Deacetylation

Human papillomaviruses (HPV) are double-stranded DNA viruses causative in a host of human diseases, including several cancers. Following infection, two viral proteins, E1 and E2, activate viral replication in association with cellular factors and stimulate the DNA damage response (DDR) during the replication process. E1-E2 uses homologous recombination (HR) to facilitate DNA replication, but an understanding of host factors involved in this process remains incomplete. Previously, we demonstrated that the class III deacetylase SIRT1, which can regulate HR, is recruited to E1-E2-replicating DNA and regulates the level of replication. Here, we demonstrate that SIRT1 promotes the fidelity of E1-E2 replication and that the absence of SIRT1 results in reduced recruitment of the DNA repair protein Werner helicase (WRN) to E1-E2-replicating DNA. CRISPR/Cas9 editing demonstrates that WRN, like SIRT1, regulates the quantity and fidelity of E1-E2 replication. This is the first report of WRN regulation of E1-E2 DNA replication, or a role for WRN in the HPV life cycle. In the absence of SIRT1 there is an increased acetylation and stability of WRN, but a reduced ability to interact with E1-E2-replicating DNA. We present a model in which E1-E2 replication turns on the DDR, stimulating SIRT1 deacetylation of WRN. This deacetylation promotes WRN interaction with E1-E2-replicating DNA to control the quantity and fidelity of replication. As well as offering a crucial insight into HPV replication control, this system offers a unique model for investigating the link between SIRT1 and WRN in controlling replication in mammalian cells.IMPORTANCE HPV16 is the major viral human carcinogen responsible for between 3 and 4% of all cancers worldwide. Following infection, this virus activates the DNA damage response (DDR) to promote its life cycle and recruits DDR proteins to its replicating DNA in order to facilitate homologous recombination during replication. This promotes the production of viable viral progeny. Our understanding of how HPV16 replication interacts with the DDR remains incomplete. Here, we demonstrate that the cellular deacetylase SIRT1, which is a part of the E1-E2 replication complex, regulates recruitment of the DNA repair protein WRN to the replicating DNA. We demonstrate that WRN regulates the level and fidelity of E1-E2 replication. Overall, the results suggest a mechanism by which SIRT1 deacetylation of WRN promotes its interaction with E1-E2-replicating DNA to control the levels and fidelity of that replication.

Fission Yeast Sirtuin Hst4 Functions in Preserving Genomic Integrity by Regulating Replisome Component Mcl1

The Schizosaccharomyces pombe sirtuin Hst4, functions in the maintenance of genome stability by regulating histone H3 lysine56 acetylation (H3K56ac) and promoting cell survival during replicative stress. However, its molecular function in DNA damage survival is unclear. Here, we show that hst4 deficiency in the fission yeast causes S phase delay and DNA synthesis defects. We identified a novel functional link between hst4 and the replisome component mcl1 in a suppressor screen aimed to identify genes that could restore the slow growth and Methyl methanesulphonate (MMS) sensitivity phenotypes of the hst4Δ mutant. Expression of the replisome component Mcl1 rescues hst4Δ phenotypes. Interestingly, hst4 and mcl1 show an epistatic interaction and suppression of hst4Δ phenotypes by mcl1 is H3K56 acetylation dependent. Furthermore, Hst4 was found to regulate the expression of mcl1. Finally, we show that hSIRT2 depletion results in decreased levels of And-1 (human orthologue of Mcl1), establishing the conservation of this mechanism. Moreover, on induction of replication stress (MMS treatment), Mcl1 levels decrease upon Hst4 down regulation. Our results identify a novel function of Hst4 in regulation of DNA replication that is dependent on H3K56 acetylation. Both SIRT2 and And-1 are deregulated in cancers. Therefore, these findings could be of therapeutic importance in future.

Phosphorylated SIRT1 associates with replication origins to prevent excess replication initiation and preserve genomic stability

Chromatin structure affects DNA replication patterns, but the role of specific chromatin modifiers in regulating the replication process is yet unclear. We report that phosphorylation of the human SIRT1 deacetylase on Threonine 530 (T530-pSIRT1) modulates DNA synthesis. T530-pSIRT1 associates with replication origins and inhibits replication from a group of 'dormant' potential replication origins, which initiate replication only when cells are subject to replication stress. Although both active and dormant origins bind T530-pSIRT1, active origins are distinguished from dormant origins by their unique association with an open chromatin mark, histone H3 methylated on lysine 4. SIRT1 phosphorylation also facilitates replication fork elongation. SIRT1 T530 phosphorylation is essential to prevent DNA breakage upon replication stress and cells harboring SIRT1 that cannot be phosphorylated exhibit a high prevalence of extrachromosomal elements, hallmarks of perturbed replication. These observations suggest that SIRT1 phosphorylation modulates the distribution of replication initiation events to insure genomic stability.

The Mcm2-7-interacting domain of human mini-chromosome maintenance 10 (Mcm10) protein is important for stable chromatin association and origin firing

The protein mini-chromosome maintenance 10 (Mcm10) was originally identified as an essential yeast protein in the maintenance of mini-chromosome plasmids. Subsequently, Mcm10 has been shown to be required for both initiation and elongation during chromosomal DNA replication. However, it is not fully understood how the multiple functions of Mcm10 are coordinated or how Mcm10 interacts with other factors at replication forks. Here, we identified and characterized the Mcm2-7-interacting domain in human Mcm10. The interaction with Mcm2-7 required the Mcm10 domain that contained amino acids 530-655, which overlapped with the domain required for the stable retention of Mcm10 on chromatin. Expression of truncated Mcm10 in HeLa cells depleted of endogenous Mcm10 via siRNA revealed that the Mcm10 conserved domain (amino acids 200-482) is essential for DNA replication, whereas both the conserved and the Mcm2-7-binding domains were required for its full activity. Mcm10 depletion reduced the initiation frequency of DNA replication and interfered with chromatin loading of replication protein A, DNA polymerase (Pol) α, and proliferating cell nuclear antigen, whereas the chromatin loading of Cdc45 and Pol ϵ was unaffected. These results suggest that human Mcm10 is bound to chromatin through the interaction with Mcm2-7 and is primarily involved in the initiation of DNA replication after loading of Cdc45 and Pol ϵ.

Mcm10: A Dynamic Scaffold at Eukaryotic Replication Forks

To complete the duplication of large genomes efficiently, mechanisms have evolved that coordinate DNA unwinding with DNA synthesis and provide quality control measures prior to cell division. Minichromosome maintenance protein 10 (Mcm10) is a conserved component of the eukaryotic replisome that contributes to this process in multiple ways. Mcm10 promotes the initiation of DNA replication through direct interactions with the cell division cycle 45 (Cdc45)-minichromosome maintenance complex proteins 2-7 (Mcm2-7)-go-ichi-ni-san GINS complex proteins, as well as single- and double-stranded DNA. After origin firing, Mcm10 controls replication fork stability to support elongation, primarily facilitating Okazaki fragment synthesis through recruitment of DNA polymerase-α and proliferating cell nuclear antigen. Based on its multivalent properties, Mcm10 serves as an essential scaffold to promote DNA replication and guard against replication stress. Under pathological conditions, Mcm10 is often dysregulated. Genetic amplification and/or overexpression of MCM10 are common in cancer, and can serve as a strong prognostic marker of poor survival. These findings are compatible with a heightened requirement for Mcm10 in transformed cells to overcome limitations for DNA replication dictated by altered cell cycle control. In this review, we highlight advances in our understanding of when, where and how Mcm10 functions within the replisome to protect against barriers that cause incomplete replication.

SIRT1 contributes to aldose reductase expression through modulating NFAT5 under osmotic stress: In vitro and in silico insights

So far, a myriad of molecules were characterized to modulate NFAT5 and its downstream targets. Among these NFAT5 modifiers, SIRT1 was proposed to have a promising role in NFAT5 dependent events, yet the exact underlying mechanism still remains obscure. Hence, the link between SIRT1 and NFAT5-aldose reductase (AR) axis under osmotic stress, was aimed to be delineated in this study. A unique osmotic stress model was generated and its mechanistic components were deciphered in U937 monocytes. In this model, AR expression and nuclear NFAT5 stabilization were revealed to be positively regulated by SIRT1 through utilization of pharmacological modulators. Overexpression and co-transfection studies of NFAT5 and SIRT1 further validated the contribution of SIRT1 to AR and NFAT5. The involvement of SIRT1 activity in these events was mediated via modification of DNA binding of NFAT5 to AR ORE region. Besides, NFAT5 and SIRT1 were also shown to co-immunoprecipitate under isosmotic conditions and this interaction was disrupted by osmotic stress. Further in silico experiments were conducted to investigate if SIRT1 directly targets NFAT5. In this regard, certain lysine residues of NFAT5, when kept deacetylated, were found to contribute to its DNA binding and SIRT1 was shown to directly bind K282 of NFAT5. Based on these in vitro and in silico findings, SIRT1 was identified, for the first time, as a novel positive regulator of NFAT5 dependent AR expression under osmotic stress in U937 monocytes.

SIRT1 deacetylates TopBP1 and modulates intra-S-phase checkpoint and DNA replication origin firing

SIRT1, the mammalian homolog of yeast Sir2, is a founding member of a family of 7 protein and histone deacetylases that are involved in numerous biological functions. Previous studies revealed that SIRT1 deficiency results in genome instability, which eventually leads to cancer formation, yet the underlying mechanism is unclear. To investigate this, we conducted a proteomics study and found that SIRT1 interacted with many proteins involved in replication fork protection and origin firing. We demonstrated that loss of SIRT1 resulted in increased replication origin firing, asymmetric fork progression, defective intra-S-phase checkpoint, and chromosome damage. Mechanistically, SIRT1 deacetylates and affects the activity of TopBP1, which plays an essential role in DNA replication fork protection and replication origin firing. Our study demonstrated that ectopic over-expression of the deacetylated form of TopBP1 in SIRT1 mutant cells repressed replication origin firing, while the acetylated form of TopBP1 lost this function. Thus, SIRT1 acts upstream of TopBP1 and plays an essential role in maintaining genome stability by modulating DNA replication fork initiation and the intra-S-phase cell cycle checkpoint.

A divergent role of the SIRT1-TopBP1 axis in regulating metabolic checkpoint and DNA damage checkpoint

DNA replication is executed only when cells have sufficient metabolic resources and undamaged DNA. Nutrient limitation and DNA damage cause a metabolic checkpoint and DNA damage checkpoint, respectively. Although SIRT1 activity is regulated by metabolic stress and DNA damage, its function in these stress-mediated checkpoints remains elusive. Here we report that the SIRT1-TopBP1 axis functions as a switch for both checkpoints. With glucose deprivation, SIRT1 is activated and deacetylates TopBP1, resulting in TopBP1-Treslin disassociation and DNA replication inhibition. Conversely, SIRT1 activity is inhibited under genotoxic stress, resulting in increased TopBP1 acetylation that is important for the TopBP1-Rad9 interaction and activation of the ATR-Chk1 pathway. Mechanistically, we showed that acetylation of TopBP1 changes the conformation of TopBP1, thereby facilitating its interaction with distinct partners in DNA replication and checkpoint activation. Taken together, our studies identify the SIRT1-TopBP1 axis as a key signaling mode in the regulation of the metabolic checkpoint and the DNA damage checkpoint.

We are ageing

Ageing and longevity is unquestioningly complex. Several thoughts and mechanisms of ageing such as pathways involved in oxidative stress, lipid and glucose metabolism, inflammation, DNA damage and repair, growth hormone axis and insulin-like growth factor (GH/IGF), and environmental exposure have been proposed. Also, some theories of ageing were introduced. To date, the most promising leads for longevity are caloric restriction, particularly target of rapamycin (TOR), sirtuins, hexarelin and hormetic responses. This review is an attempt to analyze the mechanisms and theories of ageing and achieving longevity.

MCM10: one tool for all-Integrity, maintenance and damage control

Minichromsome maintenance protein 10 (Mcm10) is an essential replication factor that is required for the activation of the Cdc45:Mcm2-7:GINS helicase. Mcm10's ability to bind both ds and ssDNA appears vital for this function. In addition, Mcm10 interacts with multiple players at the replication fork, including DNA polymerase-α and proliferating cell nuclear antigen with which it cooperates during DNA elongation. Mcm10 lacks enzymatic function, but instead provides the replication apparatus with an oligomeric scaffold that likely acts in the coordination of DNA unwinding and DNA synthesis. Not surprisingly, loss of Mcm10 engages checkpoint, DNA repair and SUMO-dependent rescue pathways that collectively counteract replication stress and chromosome breakage. Here, we review Mcm10's structure and function and explain how it contributes to the maintenance of genome integrity.

Mcm10 self-association is mediated by an N-terminal coiled-coil domain

Minichromosome maintenance protein 10 (Mcm10) is an essential eukaryotic DNA-binding replication factor thought to serve as a scaffold to coordinate enzymatic activities within the replisome. Mcm10 appears to function as an oligomer rather than in its monomeric form (or rather than as a monomer). However, various orthologs have been found to contain 1, 2, 3, 4, or 6 subunits and thus, this issue has remained controversial. Here, we show that self-association of Xenopus laevis Mcm10 is mediated by a conserved coiled-coil (CC) motif within the N-terminal domain (NTD). Crystallographic analysis of the CC at 2.4 Å resolution revealed a three-helix bundle, consistent with the formation of both dimeric and trimeric Mcm10 CCs in solution. Mutation of the side chains at the subunit interface disrupted in vitro dimerization of both the CC and the NTD as monitored by analytical ultracentrifugation. In addition, the same mutations also impeded self-interaction of the full-length protein in vivo, as measured by yeast-two hybrid assays. We conclude that Mcm10 likely forms dimers or trimers to promote its diverse functions during DNA replication.