9 research outputs found
Mécanismes de contrÎle du complexe MRX aux télomÚres
The Mre11-Rad50-Xrs2/NBS1 (MRX/N) complex is key to genome stability and double-strand break (DSB) repair. It is essential to NHEJ (Non-Homologous End-Joining) and critical for 5â resection initiation, the first step of the homologous recombination. MRX is also involved in telomere maintenance. MRX favors telomerase activity preferentially at the shortest telomeres through the Tel1/ATM kinase. MRX action at telomeres must be finely controlled to avoid telomere fusions or degradation. This control is ensured by a small set of proteins specifically enriched at chromosome ends. In the budding yeast Saccharomyces cerevisiae, the protein Rap1 directly binds telomeric repeats and recruits others factors, ensuring telomere functions. Among these proteins, Rif2 is involved in the inhibition of several functions that depend on MRX (NHEJ and 5â resection inhibition, telomerase-dependent telomere elongation). We established that a small N-terminal motif of Rif2, known to block telomere elongation, is also sufficient to inhibit NHEJ, 5â resection and MRX association to DNA ends. We identified an interaction between Rad50 ATPase domain and the Rif2 N-terminal motif. In addition, we found that the action of this motif is restricted to short distances in cis. Using structural predictions coupled to a genetic screen, we identified Rad50 residues that are essential for Rad50 interaction with Rif2 and for Rif2 ability to inhibit MRX. The position of these residues on a conserved Rad50 surface allow us to propose a model for MRX inhibition by Rif2 at telomeres. In this model, Rif2 antagonizes the MRX conformation allowing a stable association with DNA ends. In parallel, we studied the role of Rap1 in telomere protection in the absence of its partners involved in NHEJ inhibition. We established that the strength of the NHEJ inhibition by Rap1 is linked to the density and to the number of sites bound by Rap1, and to the end proximity of the Rap1 protein.Le complexe Mre11-Rad50-Xrs2/NBS1 (MRX/N) joue un rĂŽle fondamental dans le maintien de la stabilitĂ© du gĂ©nome et dans la rĂ©paration des cassures double-brin (CDB). Il est essentiel au NHEJ (Non-Homologous End-Joining), et critique pour lâinitiation de la rĂ©section 5â, premiĂšre Ă©tape de la recombinaison homologue. MRX est aussi impliquĂ© dans la maintenance des extrĂ©mitĂ©s des chromosomes. MRX favorise lâaction de la tĂ©lomĂ©rase prĂ©fĂ©rentiellement aux tĂ©lomĂšres les plus courts via lâactivation rĂ©gulĂ©e de la kinase Tel1/ATM. Lâaction de MRX aux tĂ©lomĂšres doit ĂȘtre finement contrĂŽlĂ©e pour Ă©viter une fusion ou une dĂ©gradation des tĂ©lomĂšres. Ce contrĂŽle est assurĂ© par un petit nombre de facteurs spĂ©cifiquement enrichis aux extrĂ©mitĂ©s des chromosomes. Chez la levure Saccharomyces cerevisiae, une protĂ©ine, Rap1, lie directement les rĂ©pĂ©titions tĂ©lomĂ©riques et recrute un Ă©ventail de protĂ©ines assurant les diffĂ©rentes fonctions des tĂ©lomĂšres. Parmi ces protĂ©ines, Rif2 est impliquĂ©e dans lâinhibition de plusieurs fonctions qui dĂ©pendent de MRX (inhibition du NHEJ, de la rĂ©section 5â et de lâĂ©longation des tĂ©lomĂšres par la tĂ©lomĂ©rase). Nous avons Ă©tabli quâun petit domaine N-terminal de Rif2, connu pour bloquer lâĂ©longation des tĂ©lomĂšres, Ă©tait aussi capable dâinhiber le NHEJ, la rĂ©section et le chargement du complexe MRX sur lâADN. Nous avons identifiĂ© une interaction entre les tĂȘtes ATPase de Rad50 et ce motif N-terminal de Rif2. De plus, nous avons montrĂ© que ce motif de Rif2 agit Ă courte distance en cis. Par des approches de prĂ©dictions structurales couplĂ©es Ă un crible gĂ©nĂ©tique, nous avons identifiĂ© des rĂ©sidus de Rad50 essentiels pour lâinteraction avec Rif2 et sa capacitĂ© dâinhibition du complexe. La position de ces rĂ©sidus sur une surface conservĂ©e de Rad50 nous a permis de proposer un modĂšle pour lâinhibition du complexe MRX aux tĂ©lomĂšres par Rif2, oĂč Rif2 bloque la conformation de MRX permettant lâassociation stable du complexe sur lâADN. En parallĂšle, nous avons Ă©tudiĂ© le rĂŽle de Rap1 dans la protection des tĂ©lomĂšres en lâabsence de ses partenaires impliquĂ©s dans le blocage du NHEJ. Nous avons Ă©tabli que la force de cette inhibition du NHEJ par Rap1 Ă©tait Ă©troitement liĂ©e Ă la densitĂ© et au nombre de sites fixĂ©s par Rap1, et de la proximitĂ© de Rap1 de lâextrĂ©mitĂ© dâADN
Mechanisms of MRX control at telomeres
Le complexe Mre11-Rad50-Xrs2/NBS1 (MRX/N) joue un rĂŽle fondamental dans le maintien de la stabilitĂ© du gĂ©nome et dans la rĂ©paration des cassures double-brin (CDB). Il est essentiel au NHEJ (Non-Homologous End-Joining), et critique pour lâinitiation de la rĂ©section 5â, premiĂšre Ă©tape de la recombinaison homologue. MRX est aussi impliquĂ© dans la maintenance des extrĂ©mitĂ©s des chromosomes. MRX favorise lâaction de la tĂ©lomĂ©rase prĂ©fĂ©rentiellement aux tĂ©lomĂšres les plus courts via lâactivation rĂ©gulĂ©e de la kinase Tel1/ATM. Lâaction de MRX aux tĂ©lomĂšres doit ĂȘtre finement contrĂŽlĂ©e pour Ă©viter une fusion ou une dĂ©gradation des tĂ©lomĂšres. Ce contrĂŽle est assurĂ© par un petit nombre de facteurs spĂ©cifiquement enrichis aux extrĂ©mitĂ©s des chromosomes. Chez la levure Saccharomyces cerevisiae, une protĂ©ine, Rap1, lie directement les rĂ©pĂ©titions tĂ©lomĂ©riques et recrute un Ă©ventail de protĂ©ines assurant les diffĂ©rentes fonctions des tĂ©lomĂšres. Parmi ces protĂ©ines, Rif2 est impliquĂ©e dans lâinhibition de plusieurs fonctions qui dĂ©pendent de MRX (inhibition du NHEJ, de la rĂ©section 5â et de lâĂ©longation des tĂ©lomĂšres par la tĂ©lomĂ©rase). Nous avons Ă©tabli quâun petit domaine N-terminal de Rif2, connu pour bloquer lâĂ©longation des tĂ©lomĂšres, Ă©tait aussi capable dâinhiber le NHEJ, la rĂ©section et le chargement du complexe MRX sur lâADN. Nous avons identifiĂ© une interaction entre les tĂȘtes ATPase de Rad50 et ce motif N-terminal de Rif2. De plus, nous avons montrĂ© que ce motif de Rif2 agit Ă courte distance en cis. Par des approches de prĂ©dictions structurales couplĂ©es Ă un crible gĂ©nĂ©tique, nous avons identifiĂ© des rĂ©sidus de Rad50 essentiels pour lâinteraction avec Rif2 et sa capacitĂ© dâinhibition du complexe. La position de ces rĂ©sidus sur une surface conservĂ©e de Rad50 nous a permis de proposer un modĂšle pour lâinhibition du complexe MRX aux tĂ©lomĂšres par Rif2, oĂč Rif2 bloque la conformation de MRX permettant lâassociation stable du complexe sur lâADN. En parallĂšle, nous avons Ă©tudiĂ© le rĂŽle de Rap1 dans la protection des tĂ©lomĂšres en lâabsence de ses partenaires impliquĂ©s dans le blocage du NHEJ. Nous avons Ă©tabli que la force de cette inhibition du NHEJ par Rap1 Ă©tait Ă©troitement liĂ©e Ă la densitĂ© et au nombre de sites fixĂ©s par Rap1, et de la proximitĂ© de Rap1 de lâextrĂ©mitĂ© dâADN.The Mre11-Rad50-Xrs2/NBS1 (MRX/N) complex is key to genome stability and double-strand break (DSB) repair. It is essential to NHEJ (Non-Homologous End-Joining) and critical for 5â resection initiation, the first step of the homologous recombination. MRX is also involved in telomere maintenance. MRX favors telomerase activity preferentially at the shortest telomeres through the Tel1/ATM kinase. MRX action at telomeres must be finely controlled to avoid telomere fusions or degradation. This control is ensured by a small set of proteins specifically enriched at chromosome ends. In the budding yeast Saccharomyces cerevisiae, the protein Rap1 directly binds telomeric repeats and recruits others factors, ensuring telomere functions. Among these proteins, Rif2 is involved in the inhibition of several functions that depend on MRX (NHEJ and 5â resection inhibition, telomerase-dependent telomere elongation). We established that a small N-terminal motif of Rif2, known to block telomere elongation, is also sufficient to inhibit NHEJ, 5â resection and MRX association to DNA ends. We identified an interaction between Rad50 ATPase domain and the Rif2 N-terminal motif. In addition, we found that the action of this motif is restricted to short distances in cis. Using structural predictions coupled to a genetic screen, we identified Rad50 residues that are essential for Rad50 interaction with Rif2 and for Rif2 ability to inhibit MRX. The position of these residues on a conserved Rad50 surface allow us to propose a model for MRX inhibition by Rif2 at telomeres. In this model, Rif2 antagonizes the MRX conformation allowing a stable association with DNA ends. In parallel, we studied the role of Rap1 in telomere protection in the absence of its partners involved in NHEJ inhibition. We established that the strength of the NHEJ inhibition by Rap1 is linked to the density and to the number of sites bound by Rap1, and to the end proximity of the Rap1 protein
Mécanismes de contrÎle du complexe MRX aux télomÚres
The Mre11-Rad50-Xrs2/NBS1 (MRX/N) complex is key to genome stability and double-strand break (DSB) repair. It is essential to NHEJ (Non-Homologous End-Joining) and critical for 5â resection initiation, the first step of the homologous recombination. MRX is also involved in telomere maintenance. MRX favors telomerase activity preferentially at the shortest telomeres through the Tel1/ATM kinase. MRX action at telomeres must be finely controlled to avoid telomere fusions or degradation. This control is ensured by a small set of proteins specifically enriched at chromosome ends. In the budding yeast Saccharomyces cerevisiae, the protein Rap1 directly binds telomeric repeats and recruits others factors, ensuring telomere functions. Among these proteins, Rif2 is involved in the inhibition of several functions that depend on MRX (NHEJ and 5â resection inhibition, telomerase-dependent telomere elongation). We established that a small N-terminal motif of Rif2, known to block telomere elongation, is also sufficient to inhibit NHEJ, 5â resection and MRX association to DNA ends. We identified an interaction between Rad50 ATPase domain and the Rif2 N-terminal motif. In addition, we found that the action of this motif is restricted to short distances in cis. Using structural predictions coupled to a genetic screen, we identified Rad50 residues that are essential for Rad50 interaction with Rif2 and for Rif2 ability to inhibit MRX. The position of these residues on a conserved Rad50 surface allow us to propose a model for MRX inhibition by Rif2 at telomeres. In this model, Rif2 antagonizes the MRX conformation allowing a stable association with DNA ends. In parallel, we studied the role of Rap1 in telomere protection in the absence of its partners involved in NHEJ inhibition. We established that the strength of the NHEJ inhibition by Rap1 is linked to the density and to the number of sites bound by Rap1, and to the end proximity of the Rap1 protein.Le complexe Mre11-Rad50-Xrs2/NBS1 (MRX/N) joue un rĂŽle fondamental dans le maintien de la stabilitĂ© du gĂ©nome et dans la rĂ©paration des cassures double-brin (CDB). Il est essentiel au NHEJ (Non-Homologous End-Joining), et critique pour lâinitiation de la rĂ©section 5â, premiĂšre Ă©tape de la recombinaison homologue. MRX est aussi impliquĂ© dans la maintenance des extrĂ©mitĂ©s des chromosomes. MRX favorise lâaction de la tĂ©lomĂ©rase prĂ©fĂ©rentiellement aux tĂ©lomĂšres les plus courts via lâactivation rĂ©gulĂ©e de la kinase Tel1/ATM. Lâaction de MRX aux tĂ©lomĂšres doit ĂȘtre finement contrĂŽlĂ©e pour Ă©viter une fusion ou une dĂ©gradation des tĂ©lomĂšres. Ce contrĂŽle est assurĂ© par un petit nombre de facteurs spĂ©cifiquement enrichis aux extrĂ©mitĂ©s des chromosomes. Chez la levure Saccharomyces cerevisiae, une protĂ©ine, Rap1, lie directement les rĂ©pĂ©titions tĂ©lomĂ©riques et recrute un Ă©ventail de protĂ©ines assurant les diffĂ©rentes fonctions des tĂ©lomĂšres. Parmi ces protĂ©ines, Rif2 est impliquĂ©e dans lâinhibition de plusieurs fonctions qui dĂ©pendent de MRX (inhibition du NHEJ, de la rĂ©section 5â et de lâĂ©longation des tĂ©lomĂšres par la tĂ©lomĂ©rase). Nous avons Ă©tabli quâun petit domaine N-terminal de Rif2, connu pour bloquer lâĂ©longation des tĂ©lomĂšres, Ă©tait aussi capable dâinhiber le NHEJ, la rĂ©section et le chargement du complexe MRX sur lâADN. Nous avons identifiĂ© une interaction entre les tĂȘtes ATPase de Rad50 et ce motif N-terminal de Rif2. De plus, nous avons montrĂ© que ce motif de Rif2 agit Ă courte distance en cis. Par des approches de prĂ©dictions structurales couplĂ©es Ă un crible gĂ©nĂ©tique, nous avons identifiĂ© des rĂ©sidus de Rad50 essentiels pour lâinteraction avec Rif2 et sa capacitĂ© dâinhibition du complexe. La position de ces rĂ©sidus sur une surface conservĂ©e de Rad50 nous a permis de proposer un modĂšle pour lâinhibition du complexe MRX aux tĂ©lomĂšres par Rif2, oĂč Rif2 bloque la conformation de MRX permettant lâassociation stable du complexe sur lâADN. En parallĂšle, nous avons Ă©tudiĂ© le rĂŽle de Rap1 dans la protection des tĂ©lomĂšres en lâabsence de ses partenaires impliquĂ©s dans le blocage du NHEJ. Nous avons Ă©tabli que la force de cette inhibition du NHEJ par Rap1 Ă©tait Ă©troitement liĂ©e Ă la densitĂ© et au nombre de sites fixĂ©s par Rap1, et de la proximitĂ© de Rap1 de lâextrĂ©mitĂ© dâADN
Mécanismes de contrÎle du complexe MRX aux télomÚres
The Mre11-Rad50-Xrs2/NBS1 (MRX/N) complex is key to genome stability and double-strand break (DSB) repair. It is essential to NHEJ (Non-Homologous End-Joining) and critical for 5â resection initiation, the first step of the homologous recombination. MRX is also involved in telomere maintenance. MRX favors telomerase activity preferentially at the shortest telomeres through the Tel1/ATM kinase. MRX action at telomeres must be finely controlled to avoid telomere fusions or degradation. This control is ensured by a small set of proteins specifically enriched at chromosome ends. In the budding yeast Saccharomyces cerevisiae, the protein Rap1 directly binds telomeric repeats and recruits others factors, ensuring telomere functions. Among these proteins, Rif2 is involved in the inhibition of several functions that depend on MRX (NHEJ and 5â resection inhibition, telomerase-dependent telomere elongation). We established that a small N-terminal motif of Rif2, known to block telomere elongation, is also sufficient to inhibit NHEJ, 5â resection and MRX association to DNA ends. We identified an interaction between Rad50 ATPase domain and the Rif2 N-terminal motif. In addition, we found that the action of this motif is restricted to short distances in cis. Using structural predictions coupled to a genetic screen, we identified Rad50 residues that are essential for Rad50 interaction with Rif2 and for Rif2 ability to inhibit MRX. The position of these residues on a conserved Rad50 surface allow us to propose a model for MRX inhibition by Rif2 at telomeres. In this model, Rif2 antagonizes the MRX conformation allowing a stable association with DNA ends. In parallel, we studied the role of Rap1 in telomere protection in the absence of its partners involved in NHEJ inhibition. We established that the strength of the NHEJ inhibition by Rap1 is linked to the density and to the number of sites bound by Rap1, and to the end proximity of the Rap1 protein.Le complexe Mre11-Rad50-Xrs2/NBS1 (MRX/N) joue un rĂŽle fondamental dans le maintien de la stabilitĂ© du gĂ©nome et dans la rĂ©paration des cassures double-brin (CDB). Il est essentiel au NHEJ (Non-Homologous End-Joining), et critique pour lâinitiation de la rĂ©section 5â, premiĂšre Ă©tape de la recombinaison homologue. MRX est aussi impliquĂ© dans la maintenance des extrĂ©mitĂ©s des chromosomes. MRX favorise lâaction de la tĂ©lomĂ©rase prĂ©fĂ©rentiellement aux tĂ©lomĂšres les plus courts via lâactivation rĂ©gulĂ©e de la kinase Tel1/ATM. Lâaction de MRX aux tĂ©lomĂšres doit ĂȘtre finement contrĂŽlĂ©e pour Ă©viter une fusion ou une dĂ©gradation des tĂ©lomĂšres. Ce contrĂŽle est assurĂ© par un petit nombre de facteurs spĂ©cifiquement enrichis aux extrĂ©mitĂ©s des chromosomes. Chez la levure Saccharomyces cerevisiae, une protĂ©ine, Rap1, lie directement les rĂ©pĂ©titions tĂ©lomĂ©riques et recrute un Ă©ventail de protĂ©ines assurant les diffĂ©rentes fonctions des tĂ©lomĂšres. Parmi ces protĂ©ines, Rif2 est impliquĂ©e dans lâinhibition de plusieurs fonctions qui dĂ©pendent de MRX (inhibition du NHEJ, de la rĂ©section 5â et de lâĂ©longation des tĂ©lomĂšres par la tĂ©lomĂ©rase). Nous avons Ă©tabli quâun petit domaine N-terminal de Rif2, connu pour bloquer lâĂ©longation des tĂ©lomĂšres, Ă©tait aussi capable dâinhiber le NHEJ, la rĂ©section et le chargement du complexe MRX sur lâADN. Nous avons identifiĂ© une interaction entre les tĂȘtes ATPase de Rad50 et ce motif N-terminal de Rif2. De plus, nous avons montrĂ© que ce motif de Rif2 agit Ă courte distance en cis. Par des approches de prĂ©dictions structurales couplĂ©es Ă un crible gĂ©nĂ©tique, nous avons identifiĂ© des rĂ©sidus de Rad50 essentiels pour lâinteraction avec Rif2 et sa capacitĂ© dâinhibition du complexe. La position de ces rĂ©sidus sur une surface conservĂ©e de Rad50 nous a permis de proposer un modĂšle pour lâinhibition du complexe MRX aux tĂ©lomĂšres par Rif2, oĂč Rif2 bloque la conformation de MRX permettant lâassociation stable du complexe sur lâADN. En parallĂšle, nous avons Ă©tudiĂ© le rĂŽle de Rap1 dans la protection des tĂ©lomĂšres en lâabsence de ses partenaires impliquĂ©s dans le blocage du NHEJ. Nous avons Ă©tabli que la force de cette inhibition du NHEJ par Rap1 Ă©tait Ă©troitement liĂ©e Ă la densitĂ© et au nombre de sites fixĂ©s par Rap1, et de la proximitĂ© de Rap1 de lâextrĂ©mitĂ© dâADN
Discovery and Evolution of New Domains in Yeast Heterochromatin Factor Sir4 and Its Partner Esc1
International audienceSir4 is a core component of heterochromatin found in yeasts of the Saccharomycetaceae family, whose general hallmark is to harbor a three-loci mating-type system with two silent loci. However, a large part of the Sir4 amino acid sequences has remained unexplored, belonging to the dark proteome. Here, we analyzed the phylogenetic profile of yet undescribed foldable regions present in Sir4 as well as in Esc1, an Sir4-interacting perinuclear anchoring protein. Within Sir4, we identified a new conserved motif (TOC) adjacent to the N-terminal KU-binding motif. We also found that the Esc1-interacting region of Sir4 is a Dbf4-related H-BRCT domain, only present in species possessing the HO endonuclease and in Kluveryomyces lactis. In addition, we found new motifs within Esc1 including a motif (Esc1-F) that is unique to species where Sir4 possesses an H-BRCT domain. Mutagenesis of conserved amino acids of the Sir4 H-BRCT domain, known to play a critical role in the Dbf4 function, shows that the function of this domain is separable from the essential role of Sir4 in transcriptional silencing and the protection from HO-induced cutting in Saccharomyces cerevisiae. In the more distant methylotrophic clade of yeasts, which often harbor a two-loci mating-type system with one silent locus, we also found a yet undescribed H-BRCT domain in a distinct protein, the ISWI2 chromatin-remodeling factor subunit Itc1. This study provides new insights on yeast heterochromatin evolution and emphasizes the interest of using sensitive methods of sequence analysis for identifying hitherto ignored functional regions within the dark proteome
Modulation of alternative splicing during early infection of human primary B lymphocytes with Epstein-Barr virus (EBV): a novel function for the viral EBNA-LP protein
International audienceAbstract Epstein-Barr virus (EBV) is a human herpesvirus associated with human cancers worldwide. Ex vivo, the virus efficiently infects resting human B lymphocytes and induces their continuous proliferation. This process is accompanied by a global reprogramming of cellular gene transcription. However, very little is known on the impact of EBV infection on the regulation of alternative splicing, a pivotal mechanism that plays an essential role in cell fate determination and is often deregulated in cancer. In this study, we have developed a systematic time-resolved analysis of cellular mRNA splice variant expression during EBV infection of resting B lymphocytes. Our results reveal that major modifications of alternative splice variant expression appear as early as day 1 post-infection and suggest that splicing regulation providesâbesides transcriptionâan additional mechanism of gene expression regulation at the onset of B cell activation and proliferation. We also report a role for the viral proteins, EBNA2 and EBNA-LP, in the modulation of specific alternative splicing events and reveal a previously unknown function for EBNA-LPâtogether with the RBM4 splicing factorâin the alternative splicing regulation of two important modulators of cell proliferation and apoptosis respectively, NUMB and BCL-X
Mechanism of MRX inhibition by Rif2 at telomeres
International audienceSpecific proteins present at telomeres ensure chromosome end stability, in large part through unknown mechanisms. In this work, we address how the Saccharomyces cerevisiae ORC-related Rif2 protein protects telomere. We show that the small N-terminal Rif2 BAT motif (Blocks Addition of Telomeres) previously known to limit telomere elongation and Tel1 activity is also sufficient to block NHEJ and 5' end resection. The BAT motif inhibits the ability of the Mre11-Rad50-Xrs2 complex (MRX) to capture DNA ends. It acts through a direct contact with Rad50 ATP-binding Head domains. Through genetic approaches guided by structural predictions, we identify residues at the surface of Rad50 that are essential for the interaction with Rif2 and its inhibition. Finally, a docking model predicts how BAT binding could specifically destabilise the DNA-bound state of the MRX complex. From these results, we propose that when an MRX complex approaches a telomere, the Rif2 BAT motif binds MRX Head in its ATP-bound resting state. This antagonises MRX transition to its DNA-bound state, and favours a rapid return to the ATP-bound state. Unable to stably capture the telomere end, the MRX complex cannot proceed with the subsequent steps of NHEJ, Tel1-activation and 5' resection
Avelumab Versus Docetaxel in Patients With Platinum-Treated Advanced NSCLC: 2-Year Follow-Up From the JAVELIN Lung 200 Phase 3 Trial
International audienceAbstract Specific proteins present at telomeres ensure chromosome end stability, in large part through unknown mechanisms. In this work, we address how the Saccharomyces cerevisiae ORC-related Rif2 protein protects telomere. We show that the small N-terminal Rif2 BAT motif ( B locks A ddition of T elomeres) previously known to limit telomere elongation and Tel1 activity is also sufficient to block NHEJ and 5â end resection. The BAT motif inhibits the ability of the Mre11-Rad50-Xrs2 complex (MRX) to capture DNA ends. It acts through a direct contact with Rad50 ATP-binding Head domains. Through genetic approaches guided by structural predictions, we identify residues at the surface of Rad50 that are essential for the interaction with Rif2 and its inhibition. Finally, a docking model predicts how BAT binding could specifically destabilise the DNA-bound state of the MRX complex. From these results, we propose that when an MRX complex approaches a telomere, the Rif2 BAT motif binds MRX Head in its ATP-bound resting state. This antagonises MRX transition to its DNA-bound state, and favours a rapid return to the ATP-bound state. Unable to stably capture the telomere end, the MRX complex cannot proceed with the subsequent steps of NHEJ, Tel1-activation and 5â resection