Cell-cycle-specific activators of the Mec1/ATR checkpoint kinase

2011 ◽  
Vol 39 (2) ◽  
pp. 600-605 ◽  
Author(s):  
Vasundhara M. Navadgi-Patil ◽  
Peter M. Burgers
Keyword(s):  
Cell Cycle ◽  
Replication Stress ◽  
Replication Initiation ◽  
Initiation Factor ◽  
Ataxia Telangiectasia Mutated ◽  
Checkpoint Activation ◽  
Dna Replication Initiation ◽  
G2 Phase ◽  
Two Phases ◽  
Human Rad9

Mec1 [ATR (ataxia telangiectasia mutated- and Rad3-related) in humans] is the principle kinase responsible for checkpoint activation in response to replication stress and DNA damage in Saccharomyces cerevisiae. The heterotrimeric checkpoint clamp, 9-1-1 (checkpoint clamp of Rad9, Rad1 and Hus1 in humans and Ddc1, Rad17 and Mec3 in S. cerevisiae; Ddc1-Mec3-Rad17) and the DNA replication initiation factor Dpb11 (human TopBP1) are the two known activators of Mec1. The 9-1-1 clamp functions in checkpoint activation in G1- and G2-phase, but its employment differs between these two phases of the cell cycle. The Ddc1 (human Rad9) subunit of the clamp directly activates Mec1 in G1-phase, an activity identified only in S. cerevisiae so far. However, in G2-phase, the 9-1-1 clamp activates the checkpoint by two mechanisms. One mechanism includes direct activation of Mec1 by the unstructured C-terminal tail of Ddc1. The second mech-anism involves the recruitment of Dpb11 by the phosphorylated C-terminal tail of Ddc1. The latter mechanism is highly conserved and also functions in response to replication stress in higher eukaryotes. In S. cerevisiae, however, both the 9-1-1 clamp and the Dpb11 are partially redundant for checkpoint activation in response to replication stress, suggesting the existence of additional activators of Mec1.

scholarly journals Control of DNA Rereplication via Cdc2 Phosphorylation Sites in the Origin Recognition Complex

2001 ◽  
Vol 21 (17) ◽  
pp. 5767-5777 ◽  
Author(s):  
Amit Vas ◽  
Winnie Mok ◽  
Janet Leatherwood
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Origin Recognition Complex ◽  
Safety Net ◽  
Replication Initiation ◽  
Initiation Factor ◽  
Phosphorylation Sites ◽  
Cdc2 Kinase ◽  
Origin Recognition ◽  
Dna Rereplication

ABSTRACT Cdc2 kinase is a master regulator of cell cycle progression in the fission yeast Schizosaccharomyces pombe. Our data indicate that Cdc2 phosphorylates replication factor Orp2, a subunit of the origin recognition complex (ORC). Cdc2 phosphorylation of Orp2 appears to be one of multiple mechanisms by which Cdc2 prevents DNA rereplication in a single cell cycle. Cdc2 phosphorylation of Orp2 is not required for Cdc2 to activate DNA replication initiation. Phosphorylation of Orp2 appears first in S phase and becomes maximal in G2 and M when Cdc2 kinase activity is required to prevent reinitiation of DNA replication. A mutant lacking Cdc2 phosphorylation sites in Orp2 (orp2-T4A) allowed greater rereplication of DNA than congenic orp2 wild-type strains when the limiting replication initiation factor Cdc18 was deregulated. Thus, Cdc2 phosphorylation of Orp2 may be redundant with regulation of Cdc18 for preventing reinitiation of DNA synthesis. Since Cdc2 phosphorylation sites are present in Orp2 (also known as Orc2) from yeasts to metazoans, we propose that cell cycle-regulated phosphorylation of the ORC provides a safety net to prevent DNA rereplication and resulting genetic instability.

scholarly journals Polar Remodeling and Histidine Kinase Activation, Which Is Essential for Caulobacter Cell Cycle Progression, Are Dependent on DNA Replication Initiation

2010 ◽  
Vol 192 (15) ◽  
pp. 3893-3902 ◽  
Author(s):  
Antonio A. Iniesta ◽  
Nathan J. Hillson ◽  
Lucy Shapiro
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Histidine Kinase ◽  
Cell Cycle Progression ◽  
Caulobacter Crescentus ◽  
Replication Initiation ◽  
Cycle Progression ◽  
Dna Replication Initiation ◽  
Flagellar Biosynthesis ◽  
Initiation Of Dna Replication

ABSTRACT Caulobacter crescentus initiates a single round of DNA replication during each cell cycle. Following the initiation of DNA replication, the essential CckA histidine kinase is activated by phosphorylation, which (via the ChpT phosphotransferase) enables the phosphorylation and activation of the CtrA global regulator. CtrA∼P then blocks the reinitiation of replication while regulating the transcription of a large number of cell cycle-controlled genes. It has been shown that DNA replication serves as a checkpoint for flagellar biosynthesis and cell division and that this checkpoint is mediated by the availability of active CtrA. Because CckA∼P promotes the activation of CtrA, we addressed the question of what controls the temporal activation of CckA. We found that the initiation of DNA replication is a prerequisite for remodeling the new cell pole, which includes the localization of the DivL protein kinase to that pole and, consequently, the localization, autophosphorylation, and activation of CckA at that pole. Thus, CckA activation is dependent on polar remodeling and a DNA replication initiation checkpoint that is tightly integrated with the polar phospho-signaling cascade governing cell cycle progression.

scholarly journals The Stringent Response Inhibits DNA Replication Initiation inE. coliby Modulating Supercoiling oforiC

mBio ◽  
2019 ◽  
Vol 10 (4) ◽  
Author(s):  
James A. Kraemer ◽  
Allen G. Sanderlin ◽  
Michael T. Laub
Keyword(s):  
Escherichia Coli ◽  
Dna Replication ◽  
Stringent Response ◽  
Replication Initiation ◽  
Initiation Factor ◽  
Cell Physiology ◽  
Origin Of Replication ◽  
Content Type ◽  
Dna Replication Initiation ◽  
Negative Supercoils

ABSTRACTThe stringent response enables bacteria to respond to a variety of environmental stresses, especially various forms of nutrient limitation. During the stringent response, the cell produces large quantities of the nucleotide alarmone ppGpp, which modulates many aspects of cell physiology, including reprogramming transcription, blocking protein translation, and inhibiting new rounds of DNA replication. The mechanism by which ppGpp inhibits DNA replication initiation inEscherichia coliremains unclear. Prior work suggested that ppGpp blocks new rounds of replication by inhibiting transcription of the essential initiation factordnaA, but we found that replication is still inhibited by ppGpp in cells ectopically producing DnaA. Instead, we provide evidence that a global reduction of transcription by ppGpp prevents replication initiation by modulating the supercoiling state of the origin of replication,oriC. Active transcription normally introduces negative supercoils intooriCto help promote replication initiation, so the accumulation of ppGpp reduces initiation potential atoriCby reducing transcription. We find that maintaining transcription nearoriC, either by expressing a ppGpp-blind RNA polymerase mutant or by inducing transcription from a ppGpp-insensitive promoter, can strongly bypass the inhibition of replication by ppGpp. Additionally, we show that increasing global negative supercoiling by inhibiting topoisomerase I or by deleting the nucleoid-associated protein geneseqAalso relieves inhibition. We propose a model, potentially conserved across proteobacteria, in which ppGpp indirectly creates an unfavorable energy landscape for initiation by limiting the introduction of negative supercoils intooriC.IMPORTANCETo survive bouts of starvation, cells must inhibit DNA replication. In bacteria, starvation triggers production of a signaling molecule called ppGpp (guanosine tetraphosphate) that helps reprogram cellular physiology, including inhibiting new rounds of DNA replication. While ppGpp has been known to block replication initiation inEscherichia colifor decades, the mechanism responsible was unknown. Early work suggested that ppGpp drives a decrease in levels of the replication initiator protein DnaA. However, we found that this decrease is not necessary to block replication initiation. Instead, we demonstrate that ppGpp leads to a change in DNA topology that prevents initiation. ppGpp is known to inhibit bulk transcription, which normally introduces negative supercoils into the chromosome, and negative supercoils near the origin of replication help drive its unwinding, leading to replication initiation. Thus, the accumulation of ppGpp prevents replication initiation by blocking the introduction of initiation-promoting negative supercoils. This mechanism is likely conserved throughout proteobacteria.

scholarly journals Regulation of DNA Replication Initiation by Chromosome Structure

2015 ◽  
Vol 197 (21) ◽  
pp. 3370-3377 ◽  
Author(s):  
David Magnan ◽  
David Bates
Keyword(s):  
Cell Cycle ◽  
Phase Transitions ◽  
Growth Phase ◽  
Chromosome Structure ◽  
Regulatory Mechanism ◽  
Replication Initiation ◽  
Dna Replication Initiation ◽  
Genetic Switches ◽  
Structure Density ◽  
Nucleoid Structure

Recent advancements in fluorescence imaging have shown that the bacterial nucleoid is surprisingly dynamic in terms of both behavior (movement and organization) and structure (density and supercoiling). Links between chromosome structure and replication initiation have been made in a number of species, and it is universally accepted that favorable chromosome structure is required for initiation in all cells. However, almost nothing is known about whether cells use changes in chromosome structure as a regulatory mechanism for initiation. Such changes could occur during natural cell cycle or growth phase transitions, or they could be manufactured through genetic switches of topoisomerase and nucleoid structure genes. In this review, we explore the relationship between chromosome structure and replication initiation and highlight recent work implicating structure as a regulatory mechanism. A three-component origin activation model is proposed in which thermal and topological structural elements are balanced withtrans-acting control elements (DnaA) to allow efficient initiation control under a variety of nutritional and environmental conditions. Selective imbalances in these components allow cells to block replication in response to cell cycle impasse, override once-per-cell-cycle programming during growth phase transitions, and promote reinitiation when replication forks fail to complete.

scholarly journals Chromosome remodelling by SMC/Condensin in B. subtilis is regulated by Soj/ParA during growth and sporulation

2021 ◽  
Author(s):  
David M Roberts ◽  
Anna Anchimiuk ◽  
Tomas G Kloosterman ◽  
Heath Murray ◽  
Ling Juan Wu ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Bacillus Subtilis ◽  
Chromosome Segregation ◽  
Chromosome Structure ◽  
Replication Initiation ◽  
Chromosome Organization ◽  
Filament Formation ◽  
Axial Filament ◽  
Dna Replication Initiation ◽  
The Web

SMC complexes, loaded at ParB-parS sites, are key mediators of chromosome organization in bacteria. ParA/Soj proteins interact with ParB/Spo0J in a pathway involving ATP-dependent dimerization and DNA binding, leading to chromosome segregation and SMC loading. In Bacillus subtilis, ParA/Soj also regulates DNA replication initiation, and along with ParB/Spo0J is involved in cell cycle changes during endospore formation. The first morphological stage in sporulation is the formation of an elongated chromosome structure called an axial filament. We now show that a major redistribution of SMC complexes drives axial filament formation, in a process regulated by ParA/Soj. Unexpectedly, this regulation is dependent on monomeric forms of ParA/Soj that cannot bind DNA or hydrolyse ATP. These results reveal a new role for ParA/Soj proteins in the regulation of SMC dynamics in bacteria, and yet further complexity in the web of interactions involving chromosome replication, segregation, and organization, controlled by ParAB and SMC.

scholarly journals Cell Cycle-Dependent Switch of TopBP1 Functions by Cdk2 and Akt

2020 ◽  
Vol 40 (8) ◽  
Author(s):  
Kang Liu ◽  
Joshua D. Graves ◽  
Yu-Ju Lee ◽  
Fang-Tsyr Lin ◽  
Weei-Chin Lin
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Cancer Cells ◽  
Cyclin A ◽  
Replication Initiation ◽  
Dna Replication Initiation ◽  
Cycle Dependent

ABSTRACT Cdk2-dependent TopBP1-treslin interaction is critical for DNA replication initiation. However, it remains unclear how this association is terminated after replication initiation is finished. Here, we demonstrate that phosphorylation of TopBP1 by Akt coincides with cyclin A activation during S and G2 phases and switches the TopBP1-interacting partner from treslin to E2F1, which results in the termination of replication initiation. Premature activation of Akt in G1 phase causes an early switch and inhibits DNA replication. TopBP1 is often overexpressed in cancer and can bypass control by Cdk2 to interact with treslin, leading to enhanced DNA replication. Consistent with this notion, reducing the levels of TopBP1 in cancer cells restores sensitivity to a Cdk2 inhibitor. Together, our study links Cdk2 and Akt pathways to the control of DNA replication through the regulation of TopBP1-treslin interaction. These data also suggest an important role for TopBP1 in driving abnormal DNA replication in cancer.

scholarly journals Control of DNA Replication Initiation by Ubiquitin

Cells ◽  
2018 ◽  
Vol 7 (10) ◽  
pp. 146 ◽  
Author(s):  
Esperanza Hernández-Carralero ◽  
Elisa Cabrera ◽  
Ignacio Alonso-de Vega ◽  
Santiago Hernández-Pérez ◽  
Veronique Smits ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Replication Initiation ◽  
Post Translational Modifications ◽  
Precise Control ◽  
Dna Replication Initiation ◽  
Fundamental Part ◽  
Initiation Of Dna Replication ◽  
The Right ◽  
Hydrolysis Of

Eukaryotic cells divide by accomplishing a program of events in which the replication of the genome is a fundamental part. To ensure all cells have an accurate copy of the genome, DNA replication occurs only once per cell cycle and is controlled by numerous pathways. A key step in this process is the initiation of DNA replication in which certain regions of DNA are marked as competent to replicate. Moreover, initiation of DNA replication needs to be coordinated with other cell cycle processes. At the molecular level, initiation of DNA replication relies, among other mechanisms, upon post-translational modifications, including the conjugation and hydrolysis of ubiquitin. An example is the precise control of the levels of the DNA replication initiation protein Cdt1 and its inhibitor Geminin by ubiquitin-mediated proteasomal degradation. This control ensures that DNA replication occurs with the right timing during the cell cycle, thereby avoiding re-replication events. Here, we review the events that involve ubiquitin signalling during DNA replication initiation, and how they are linked to human disease.

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