scholarly journals MCM Paradox: Abundance of Eukaryotic Replicative Helicases and Genomic Integrity

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Mitali Das ◽  
Sunita Singh ◽  
Satyajit Pradhan ◽  
Gopeshwar Narayan
Keyword(s):  
Distribution Patterns ◽  
Threshold Level ◽  
Genomic Integrity ◽  
Future Prospects ◽  
Minichromosome Maintenance ◽  
Replicative Helicase ◽  
Crucial Component ◽  
Eukaryotic Dna ◽  
Mcm Proteins ◽  
Insight Into

As a crucial component of DNA replication licensing system, minichromosome maintenance (MCM) 2–7 complex acts as the eukaryotic DNA replicative helicase. The six related MCM proteins form a heterohexamer and bind with ORC, CDC6, and Cdt1 to form the prereplication complex. Although the MCMs are well known as replicative helicases, their overabundance and distribution patterns on chromatin present a paradox called the “MCM paradox.” Several approaches had been taken to solve the MCM paradox and describe the purpose of excess MCMs distributed beyond the replication origins. Alternative functions of these MCMs rather than a helicase had also been proposed. This review focuses on several models and concepts generated to solve the MCM paradox coinciding with their helicase function and provides insight into the concept that excess MCMs are meant for licensing dormant origins as a backup during replication stress. Finally, we extend our view towards the effect of alteration of MCM level. Though an excess MCM constituent is needed for normal cells to withstand stress, there must be a delineation of the threshold level in normal and malignant cells. This review also outlooks the future prospects to better understand the MCM biology.

The MCM complex: (just) a replicative helicase?

2008 ◽  
Vol 36 (1) ◽  
pp. 136-140 ◽  
Author(s):  
Alessandro Costa ◽  
Silvia Onesti
Keyword(s):  
Minichromosome Maintenance ◽  
Replicative Helicase ◽  
Aaa Atpase ◽  
Mcm Helicase ◽  
Eukaryotic Dna ◽  
Mcm Complex ◽  
Elongation Step ◽  
Hexameric Helicases

The MCM2–MCM7 (minichromosome maintenance 2–7) complex is involved both in the initiation and the elongation step of eukaryotic DNA replication and is believed to be the replicative helicase. Whereas the mechanism of DNA unwinding at the replication fork has been extensively investigated, the role of the MCM2–MCM7 complex during initiation has not yet been characterized by biochemical studies. Here we summarize the in vivo evidence which supports a role for the MCM complex in origin melting. In addition, we present an overview of the mechanism of action of a number of AAA+ (ATPase associated with various cellular activities) initiators and hexameric helicases, which can be used in turn as models for the steps of recognition, duplex melting, loading and nucleic acid translocation of the MCM helicase.

scholarly journals An archaeal order with multiple minichromosome maintenance genes

Microbiology ◽  
2010 ◽  
Vol 156 (5) ◽  
pp. 1405-1414 ◽  
Author(s):  
Alison D. Walters ◽  
James P. J. Chong
Keyword(s):  
Escherichia Coli ◽  
Molecular Mechanisms ◽  
The Other ◽  
Minichromosome Maintenance ◽  
Methanococcus Maripaludis ◽  
Replicative Helicase ◽  
Molecular Studies ◽  
Mcm Proteins ◽  
Genome Context

In eukaryotes, a complex of six highly related minichromosome maintenance (MCM) proteins is believed to function as the replicative helicase. Until recently, systems for exploring the molecular mechanisms underlying eukaryotic MCM function have been biochemically intractable. To overcome this, molecular studies of MCM function have been carried out using MCM homologues from the archaea. Archaeal MCM systems studied to date possess a single functional MCM, which forms a homohexameric complex that displays DNA binding, ATPase and helicase activities. We have identified an archaeal order that possesses multiple MCM homologues. blast searches of available Methanococcales genomes reveal that members of this order possess between two and eight MCM homologues. Phylogenetic analysis suggests that an ancient duplication in the Methanococcales gave rise to two major groups of MCMs. One group contains Methanococcus maripaludis S2 McmD and possesses a conserved C-terminal insert similar to one observed in eukaryotic MCM3, while the other group contains McmA, -B and -C. Analysis of the genome context of MCMs in the latter group indicates that these genes could have arisen from phage-mediated events. When co-expressed in Escherichia coli, the four MCMs from M. maripaludis co-purify, indicating the formation of heteromeric complexes in vitro. The presence of homologues from both groups in all Methanococcales indicates that there could be functionally important differences between these proteins and that Methanococcales MCMs may therefore provide an interesting additional model for eukaryotic MCM function.

scholarly journals The eukaryotic replisome requires an additional helicase to disarm dormant replication origins

2020 ◽  
Author(s):  
Jake Hill ◽  
Patrik Eickhoff ◽  
Lucy S. Drury ◽  
Alessandro Costa ◽  
John F.X. Diffley
Keyword(s):  
Replication Fork ◽  
S Phase ◽  
Replication Forks ◽  
Minichromosome Maintenance ◽  
Double Stranded Dna ◽  
Efficient Replication ◽  
Eukaryotic Dna ◽  
Mcm Proteins ◽  
Fork Stalling ◽  
Pif1 Helicase

Origins of eukaryotic DNA replication are ‘licensed’ during G1 phase of the cell cycle by loading the six related minichromosome maintenance (MCM) proteins into a double hexameric ring around double-stranded DNA. In S phase, some double hexamers (MCM DHs) are converted into active CMG (Cdc45-MCM-GINS) helicases which nucleate assembly of bidirectional replication forks. The remaining unfired MCM DHs act as ‘dormant’ origins to provide backup replisomes in the event of replication fork stalling. The fate of unfired MCM DHs during replication is unknown. Here we show that active replisomes cannot remove unfired MCM DHs. Instead, they are pushed ahead of the replisome where they prevent fork convergence during replication termination and replisome progression through nucleosomes. Pif1 helicase, together with the replisome, can remove unfired MCM DHs specifically from replicating DNA, allowing efficient replication and termination. Our results provide an explanation for how excess replication license is removed during S phase.

scholarly journals The eukaryotic replisome requires an additional helicase to disarm dormant replication origins

2020 ◽  
Author(s):  
Jake Hill ◽  
Patrik Eickhoff ◽  
Lucy Drury ◽  
Alessandro Costa ◽  
John Diffley
Keyword(s):  
Replication Fork ◽  
S Phase ◽  
Replication Forks ◽  
Minichromosome Maintenance ◽  
Double Stranded Dna ◽  
Efficient Replication ◽  
Eukaryotic Dna ◽  
Mcm Proteins ◽  
Fork Stalling ◽  
Pif1 Helicase

Abstract Origins of eukaryotic DNA replication are ‘licensed’ during G1 phase of the cell cycle by loading the six related minichromosome maintenance (MCM) proteins into a double hexameric ring around double-stranded DNA. In S phase, some double hexamers (MCM DHs) are converted into active CMG (Cdc45-MCM-GINS) helicases which nucleate assembly of bidirectional replication forks. The remaining unfired MCM DHs act as ‘dormant’ origins to provide backup replisomes in the event of replication fork stalling. The fate of unfired MCM DHs during replication is unknown. Here we show that active replisomes cannot remove unfired MCM DHs. Instead, they are pushed ahead of the replisome where they prevent fork convergence during replication termination and replisome progression through nucleosomes. Pif1 helicase, together with the replisome, can remove unfired MCM DHs specifically from replicating DNA, allowing efficient replication and termination. Our results provide an explanation for how excess replication license is removed during S phase.

scholarly journals Essential Role of MCM Proteins in Premeiotic DNA Replication

2002 ◽  
Vol 13 (2) ◽  
pp. 435-444 ◽  
Author(s):  
Karola Lindner ◽  
Juraj Gregán ◽  
Stuart Montgomery ◽  
Stephen E. Kearsey
Keyword(s):  
Dna Replication ◽  
S Phase ◽  
Yeast Cells ◽  
Critical Event ◽  
Minichromosome Maintenance ◽  
Cell Cycles ◽  
Eukaryotic Dna ◽  
Mcm Proteins ◽  
Meiotic Cycle

A critical event in eukaryotic DNA replication involves association of minichromosome maintenance (MCM2–7) proteins with origins, to form prereplicative complexes (pre-RCs) that are competent for initiation. The ability of mutants defective in MCM2–7 function to complete meiosis had suggested that pre-RC components could be irrelevant to premeiotic S phase. We show here that MCM2–7 proteins bind to chromatin in fission yeast cells preparing for meiosis and during premeiotic S phase in a manner suggesting they in fact are required for DNA replication in the meiotic cycle. This is confirmed by analysis of a degron mcm4 mutant, which cannot carry out premeiotic DNA replication. Later in meiosis, Mcm4 chromatin association is blocked between meiotic nuclear divisions, presumably accounting for the absence of a second round of DNA replication. Together, these results emphasize similarity between replication mechanisms in mitotic and meiotic cell cycles.

scholarly journals Ciprofloxacin is an inhibitor of the Mcm2-7 replicative helicase

2013 ◽  
Vol 33 (5) ◽  
Author(s):  
Nicholas Simon ◽  
Matthew L. Bochman ◽  
Sandlin Seguin ◽  
Jeffrey L. Brodsky ◽  
William L. Seibel ◽  
...  
Keyword(s):  
Dna Replication ◽  
Dna Helicase ◽  
Dna Unwinding ◽  
Helicase Activity ◽  
Minichromosome Maintenance ◽  
Replicative Helicase ◽  
Eukaryotic Dna ◽  
Minichromosome Maintenance Protein ◽  
Ciprofloxacin Resistance

Most currently available small molecule inhibitors of DNA replication lack enzymatic specificity, resulting in deleterious side effects during use in cancer chemotherapy and limited experimental usefulness as mechanistic tools to study DNA replication. Towards development of targeted replication inhibitors, we have focused on Mcm2-7 (minichromosome maintenance protein 2–7), a highly conserved helicase and key regulatory component of eukaryotic DNA replication. Unexpectedly we found that the fluoroquinolone antibiotic ciprofloxacin preferentially inhibits Mcm2-7. Ciprofloxacin blocks the DNA helicase activity of Mcm2-7 at concentrations that have little effect on other tested helicases and prevents the proliferation of both yeast and human cells at concentrations similar to those that inhibit DNA unwinding. Moreover, a previously characterized mcm mutant (mcm4chaos3) exhibits increased ciprofloxacin resistance. To identify more potent Mcm2-7 inhibitors, we screened molecules that are structurally related to ciprofloxacin and identified several that compromise the Mcm2-7 helicase activity at lower concentrations. Our results indicate that ciprofloxacin targets Mcm2-7 in vitro, and support the feasibility of developing specific quinolone-based inhibitors of Mcm2-7 for therapeutic and experimental applications.

scholarly journals Bi-allelic MCM10 variants associated with immune dysfunction and cardiomyopathy cause telomere shortening

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ryan M. Baxley ◽  
Wendy Leung ◽  
Megan M. Schmit ◽  
Jacob Peter Matson ◽  
Lulu Yin ◽  
...  
Keyword(s):  
Immune Cell ◽  
Nk Cell ◽  
Restrictive Cardiomyopathy ◽  
Telomerase Activity ◽  
Compound Heterozygous ◽  
Minichromosome Maintenance ◽  
Telomere Shortening ◽  
Clinical Phenotypes ◽  
Eukaryotic Dna ◽  
Minichromosome Maintenance Protein

AbstractMinichromosome maintenance protein 10 (MCM10) is essential for eukaryotic DNA replication. Here, we describe compound heterozygous MCM10 variants in patients with distinctive, but overlapping, clinical phenotypes: natural killer (NK) cell deficiency (NKD) and restrictive cardiomyopathy (RCM) with hypoplasia of the spleen and thymus. To understand the mechanism of MCM10-associated disease, we modeled these variants in human cell lines. MCM10 deficiency causes chronic replication stress that reduces cell viability due to increased genomic instability and telomere erosion. Our data suggest that loss of MCM10 function constrains telomerase activity by accumulating abnormal replication fork structures enriched with single-stranded DNA. Terminally-arrested replication forks in MCM10-deficient cells require endonucleolytic processing by MUS81, as MCM10:MUS81 double mutants display decreased viability and accelerated telomere shortening. We propose that these bi-allelic variants in MCM10 predispose specific cardiac and immune cell lineages to prematurely arrest during differentiation, causing the clinical phenotypes observed in both NKD and RCM patients.

scholarly journals Atypical cutaneous and musculoskeletal manifestation of SARS-CoV-2: ‘COVID-19 toes’ and spasticity in a 48-year-old woman

2021 ◽  
Vol 14 (3) ◽  
pp. e241410
Author(s):  
Avery Kopacz ◽  
Cameron Ludwig ◽  
Michelle Tarbox
Keyword(s):  
Nervous System ◽  
Adult Patient ◽  
Early Identification ◽  
Lower Limbs ◽  
Rare Occurrence ◽  
Cutaneous Manifestations ◽  
Crucial Component ◽  
History Of ◽  
Screening Questions ◽  
Insight Into

Establishing accurate symptomatology associated with novel diseases such as COVID-19 is a crucial component of early identification and screening. This case report identifies an adult patient with a history of clotting dysfunction presenting with rare cutaneous manifestations of COVID-19, known as ‘COVID-19 toes’', previously described predominantly in children. Additionally, this patient presented with possible COVID-associated muscle spasticity of the lower limbs, as well as a prolonged and atypical timeline of COVID-19 infection. The rare occurrence of ‘COVID-19 toes’' in this adult patient suggests that her medical history could have predisposed her to this symptom. This supports the coagulopathic hypothesis of this manifestation of COVID-19 and provides possible screening questions for patients with a similar history who might be exposed to the virus. Additionally, nervous system complaints associated with this disease are rare and understudied, so this novel symptom may also provide insight into this aspect of SARS-CoV-2.

scholarly journals DNA Unwinding Is an MCM Complex-dependent and ATP Hydrolysis-dependent Process

2004 ◽  
Vol 279 (44) ◽  
pp. 45586-45593 ◽  
Author(s):  
David Shechter ◽  
Carol Y. Ying ◽  
Jean Gautier
Keyword(s):  
Dna Replication ◽  
Neutralizing Antibodies ◽  
Atp Hydrolysis ◽  
Initial Period ◽  
Dna Helicase ◽  
Dna Unwinding ◽  
Origin Firing ◽  
Replicative Helicase ◽  
Mcm Proteins

Minichromosome maintenance proteins (Mcm) are essential in all eukaryotes and are absolutely required for initiation of DNA replication. The eukaryotic and archaeal Mcm proteins have conserved helicase motifs and exhibit DNA helicase and ATP hydrolysis activitiesin vitro. Although the Mcm proteins have been proposed to be the replicative helicase, the enzyme that melts the DNA helix at the replication fork, their function during cellular DNA replication elongation is still unclear. Using nucleoplasmic extract (NPE) fromXenopus laeviseggs and six purified polyclonal antibodies generated against each of theXenopusMcm proteins, we have demonstrated that Mcm proteins are required during DNA replication and DNA unwinding after initiation of replication. Quantitative depletion of Mcms from the NPE results in normal replication and unwinding, confirming that Mcms are required before pre-replicative complex assembly and dispensable thereafter. Replication and unwinding are inhibited when pooled neutralizing antibodies against the six different Mcm2–7 proteins are added during NPE incubation. Furthermore, replication is blocked by the addition of the Mcm antibodies after an initial period of replication in the NPE, visualized by a pulse of radiolabeled nucleotide at the same time as antibody addition. Addition of the cyclin-dependent kinase 2 inhibitor p21cip1specifically blocks origin firing but does not prevent helicase action. When p21cip1is added, followed by the non-hydrolyzable analog ATPγS to block helicase function, unwinding is inhibited, demonstrating that plasmid unwinding is specifically attributable to an ATP hydrolysis-dependent function. These data support the hypothesis that the Mcm protein complex functions as the replicative helicase.

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