The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Ralph Scully - One of the best experts on this subject based on the ideXlab platform.
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xrcc2 and xrcc3 regulate the balance between short and long tract gene conversions between Sister Chromatids
Molecular and Cellular Biology, 2009Co-Authors: Ganesh Nagaraju, Andrea J Hartlerode, Amy Kwok, Gurushankar Chandramouly, Ralph ScullyAbstract:Sister chromatid recombination (SCR) is a potentially error-free pathway for the repair of DNA lesions associated with replication and is thought to be important for suppressing genomic instability. The mechanisms regulating the initiation and termination of SCR in mammalian cells are poorly understood. Previous work has implicated all the Rad51 paralogs in the initiation of gene conversion and the Rad51C/XRCC3 complex in its termination. Here, we show that hamster cells deficient in the Rad51 paralog XRCC2, a component of the Rad51B/Rad51C/Rad51D/XRCC2 complex, reveal a bias in favor of long-tract gene conversion (LTGC) during SCR. This defect is corrected by expression of wild-type XRCC2 and also by XRCC2 mutants defective in ATP binding and hydrolysis. In contrast, XRCC3-mediated homologous recombination and suppression of LTGC are dependent on ATP binding and hydrolysis. These results reveal an unexpectedly general role for Rad51 paralogs in the control of the termination of gene conversion between Sister Chromatids.
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differential regulation of short and long tract gene conversion between Sister Chromatids by rad51c
Molecular and Cellular Biology, 2006Co-Authors: Ganesh Nagaraju, Shobu Odate, Ralph ScullyAbstract:The Rad51 paralog Rad51C has been implicated in the control of homologous recombination. To study the role of Rad51C in vivo in mammalian cells, we analyzed short-tract and long-tract gene conversion between Sister Chromatids in hamster Rad51C / CL-V4B cells in response to a site-specific chromosomal doublestrand break. Gene conversion was inefficient in these cells and was specifically restored by expression of wild-type Rad51C. Surprisingly, gene conversions in CL-V4B cells were biased in favor of long-tract gene conversion, in comparison to controls expressing wild-type Rad51C. These long-tract events were not associated with crossing over between Sister Chromatids. Analysis of gene conversion tract lengths in CL-V4B cells lacking Rad51C revealed a bimodal frequency distribution, with almost all gene conversions being either less than 1 kb or greater than 3.2 kb in length. These results indicate that Rad51C plays a pivotal role in determining the “choice” between short- and long-tract gene conversion and in suppressing gene amplifications associated with Sister chromatid recombination. Double-strand breaks (DSB) are a threat to genome stability, since their misrepair can cause chromosome translocations,
Ganesh Nagaraju - One of the best experts on this subject based on the ideXlab platform.
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xrcc2 and xrcc3 regulate the balance between short and long tract gene conversions between Sister Chromatids
Molecular and Cellular Biology, 2009Co-Authors: Ganesh Nagaraju, Andrea J Hartlerode, Amy Kwok, Gurushankar Chandramouly, Ralph ScullyAbstract:Sister chromatid recombination (SCR) is a potentially error-free pathway for the repair of DNA lesions associated with replication and is thought to be important for suppressing genomic instability. The mechanisms regulating the initiation and termination of SCR in mammalian cells are poorly understood. Previous work has implicated all the Rad51 paralogs in the initiation of gene conversion and the Rad51C/XRCC3 complex in its termination. Here, we show that hamster cells deficient in the Rad51 paralog XRCC2, a component of the Rad51B/Rad51C/Rad51D/XRCC2 complex, reveal a bias in favor of long-tract gene conversion (LTGC) during SCR. This defect is corrected by expression of wild-type XRCC2 and also by XRCC2 mutants defective in ATP binding and hydrolysis. In contrast, XRCC3-mediated homologous recombination and suppression of LTGC are dependent on ATP binding and hydrolysis. These results reveal an unexpectedly general role for Rad51 paralogs in the control of the termination of gene conversion between Sister Chromatids.
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differential regulation of short and long tract gene conversion between Sister Chromatids by rad51c
Molecular and Cellular Biology, 2006Co-Authors: Ganesh Nagaraju, Shobu Odate, Ralph ScullyAbstract:The Rad51 paralog Rad51C has been implicated in the control of homologous recombination. To study the role of Rad51C in vivo in mammalian cells, we analyzed short-tract and long-tract gene conversion between Sister Chromatids in hamster Rad51C / CL-V4B cells in response to a site-specific chromosomal doublestrand break. Gene conversion was inefficient in these cells and was specifically restored by expression of wild-type Rad51C. Surprisingly, gene conversions in CL-V4B cells were biased in favor of long-tract gene conversion, in comparison to controls expressing wild-type Rad51C. These long-tract events were not associated with crossing over between Sister Chromatids. Analysis of gene conversion tract lengths in CL-V4B cells lacking Rad51C revealed a bimodal frequency distribution, with almost all gene conversions being either less than 1 kb or greater than 3.2 kb in length. These results indicate that Rad51C plays a pivotal role in determining the “choice” between short- and long-tract gene conversion and in suppressing gene amplifications associated with Sister chromatid recombination. Double-strand breaks (DSB) are a threat to genome stability, since their misrepair can cause chromosome translocations,
Kim Nasmyth - One of the best experts on this subject based on the ideXlab platform.
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Splitting the chromosome: cutting the ties that bind Sister Chromatids.
Novartis Foundation Symposium, 2008Co-Authors: Kim Nasmyth, Janmichael Peters, Frank UhlmannAbstract:: In eukaryotic cells, replicated DNA molecules remain physically connected from their synthesis in S phase until they are separated during anaphase. This phenomenon, called Sister chromatid cohesion, is essential for the temporal separation of DNA replication and mitosis and for the equal separation of the duplicated genome. Recent work has identified a number of chromosomal proteins required for cohesion. In this review we discuss how these proteins may connect Sister Chromatids and how they are removed from chromosomes to allow Sister chromatid separation at the onset of anaphase.
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Building and breaking bridges between Sister Chromatids
BioEssays, 2003Co-Authors: Christian H. Haering, Kim NasmythAbstract:Eukaryotic chromosomes undergo dramatic changes and movements during mitosis. These include the individualization and compaction of the two copies of replicated chromosomes (the Sister Chromatids) and their subsequent segregation to the daughter cells. Two multisubunit protein complexes termed ‘cohesin’ and ‘condensin’, both composed of SMC (Structural Maintenance of Chromosomes) and kleisin subunits, have emerged as crucial players in these processes. Cohesin is required for holding Sister Chromatids together whereas condensin, together with topoisomerase II, has an important role in organizing individual axes of Sister Chromatids prior to their segregation during anaphase. SMC and kleisin complexes also regulate the compaction and segregation of bacterial nucleoids. New research suggests that these ancient regulators of chromosome structure might function as topological devices that trap chromosomal DNA between 50 nm long coiled coils. BioEssays 25:1178–1191, 2003. © 2003 Wiley Periodicals, Inc.
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disseminating the genome joining resolving and separating Sister Chromatids during mitosis and meiosis
Annual Review of Genetics, 2001Co-Authors: Kim NasmythAbstract:▪ Abstract The separation of Sister Chromatids at the metaphase to anaphase transition is one of the most dramatic of all cellular events and is a crucial aspect of all sexual and asexual reproduction. The molecular basis for this process has until recently remained obscure. New research has identified proteins that hold Sisters together while they are aligned on the metaphase plate. It has also shed insight into the mechanisms that dissolve Sister chromatid cohesion during both mitosis and meiosis. These findings promise to provide insights into defects in chromosome segregation that occur in cancer cells and into the pathological pathways by which aneuploidy arises during meiosis.
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splitting the chromosome cutting the ties that bind Sister Chromatids
Science, 2000Co-Authors: Kim Nasmyth, Janmichael Peters, Frank UhlmannAbstract:In eukaryotic cells, Sister DNA molecules remain physically connected from their production at S phase until their separation during anaphase. This cohesion is essential for the separation of Sister Chromatids to opposite poles of the cell at mitosis. It also permits chromosome segregation to take place long after duplication has been completed. Recent work has identified a multisubunit complex called cohesin that is essential for connecting Sisters. Proteolytic cleavage of one of cohesin's subunits may trigger Sister separation at the onset of anaphase.
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separating Sister Chromatids
Trends in Biochemical Sciences, 1999Co-Authors: Kim NasmythAbstract:Abstract Loss of cohesion between Sister Chromatids triggers their segregation during anaphase. Recent work has identified both a cohesin complex that holds Sisters together and a Sister-separating protein, separin, that destroys cohesion. Separins are bound by inhibitory proteins whose proteolysis at the metaphase–anaphase transition is mediated by the anaphase-promoting complex and its activator protein CDC20 (APC CDC20 ). When chromosomes are misaligned, a surveillance mechanism (checkpoint) blocks Sister separation by inhibiting APC CDC20 . Defects in this apparatus are implicated in causing aneuploidy in human cells.
Vincent Guacci - One of the best experts on this subject based on the ideXlab platform.
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cohesin independent segregation of Sister Chromatids in budding yeast
Molecular Biology of the Cell, 2012Co-Authors: Vincent Guacci, Douglas KoshlandAbstract:: Cohesin generates cohesion between Sister Chromatids, which enables chromosomes to form bipolar attachments to the mitotic spindle and segregate. Cohesin also functions in chromosome condensation, transcriptional regulation, and DNA damage repair. Here we analyze the role of acetylation in modulating cohesin functions and how it affects budding yeast viability. Previous studies show that cohesion establishment requires Eco1p-mediated acetylation of the cohesin subunit Smc3p at residue K113. Smc3p acetylation was proposed to promote establishment by merely relieving Wpl1p inhibition because deletion of WPL1 bypasses the lethality of an ECO1 deletion (eco1Δ wpl1Δ). We find that little, if any, cohesion is established in eco1Δ wpl1Δ cells, indicating that Eco1p performs a function beyond antagonizing Wpl1p. Cohesion also fails to be established when SMC3 acetyl-mimics (K113Q or K112R,K113Q) are the sole functional SMC3s in cells. These results suggest that Smc3p acetylation levels affect establishment. It is remarkable that, despite their severe cohesion defect, eco1Δ wpl1Δ and smc3-K112R,K113Q strains are viable because a cohesin-independent mechanism enables bipolar attachment and segregation. This alternative mechanism is insufficient for smc3-K113Q strain viability. Smc3-K113Q is defective for condensation, whereas eco1Δ wpl1Δ and smc3-K112R,K113Q strains are competent for condensation. We suggest that Smc3p acetylation and Wpl1p antagonistically regulate cohesin's essential role in condensation.
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pds5 is required for homologue pairing and inhibits synapsis of Sister Chromatids during yeast meiosis
Journal of Cell Biology, 2009Co-Authors: Vincent Guacci, Hongguo YuAbstract:During meiosis, homologues become juxtaposed and synapsed along their entire length. Mutations in the cohesin complex disrupt not only Sister chromatid cohesion but also homologue pairing and synaptonemal complex formation. In this study, we report that Pds5, a cohesin-associated protein known to regulate Sister chromatid cohesion, is required for homologue pairing and synapsis in budding yeast. Pds5 colocalizes with cohesin along the length of meiotic chromosomes. In the absence of Pds5, the meiotic cohesin subunit Rec8 remains bound to chromosomes with only minor defects in Sister chromatid cohesion, but Sister Chromatids synapse instead of homologues. Double-strand breaks (DSBs) are formed but are not repaired efficiently. In addition, meiotic chromosomes undergo hypercondensation. When the mitotic cohesin subunit Mcd1 is substituted for Rec8 in Pds5-depleted cells, chromosomes still hypercondense, but synapsis of Sister Chromatids is abolished. These data suggest that Pds5 modulates the Rec8 activity to facilitate chromosome morphological changes required for homologue synapsis, DSB repair, and meiotic chromosome segregation.
Douglas Koshland - One of the best experts on this subject based on the ideXlab platform.
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cohesin independent segregation of Sister Chromatids in budding yeast
Molecular Biology of the Cell, 2012Co-Authors: Vincent Guacci, Douglas KoshlandAbstract:: Cohesin generates cohesion between Sister Chromatids, which enables chromosomes to form bipolar attachments to the mitotic spindle and segregate. Cohesin also functions in chromosome condensation, transcriptional regulation, and DNA damage repair. Here we analyze the role of acetylation in modulating cohesin functions and how it affects budding yeast viability. Previous studies show that cohesion establishment requires Eco1p-mediated acetylation of the cohesin subunit Smc3p at residue K113. Smc3p acetylation was proposed to promote establishment by merely relieving Wpl1p inhibition because deletion of WPL1 bypasses the lethality of an ECO1 deletion (eco1Δ wpl1Δ). We find that little, if any, cohesion is established in eco1Δ wpl1Δ cells, indicating that Eco1p performs a function beyond antagonizing Wpl1p. Cohesion also fails to be established when SMC3 acetyl-mimics (K113Q or K112R,K113Q) are the sole functional SMC3s in cells. These results suggest that Smc3p acetylation levels affect establishment. It is remarkable that, despite their severe cohesion defect, eco1Δ wpl1Δ and smc3-K112R,K113Q strains are viable because a cohesin-independent mechanism enables bipolar attachment and segregation. This alternative mechanism is insufficient for smc3-K113Q strain viability. Smc3-K113Q is defective for condensation, whereas eco1Δ wpl1Δ and smc3-K112R,K113Q strains are competent for condensation. We suggest that Smc3p acetylation and Wpl1p antagonistically regulate cohesin's essential role in condensation.
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A multi-step pathway for the establishment of Sister chromatid cohesion.
PLOS Genetics, 2006Co-Authors: Mark Milutinovich, Robert V. Skibbens, Elçin Ünal, Christopher S. Ward, Douglas KoshlandAbstract:The cohesion of Sister Chromatids is mediated by cohesin, a protein complex containing members of the structural maintenance of chromosome (Smc) family. How cohesins tether Sister Chromatids is not yet understood. Here, we mutate SMC1, the gene encoding a cohesin subunit of budding yeast, by random insertion dominant negative mutagenesis to generate alleles that are highly informative for cohesin assembly and function. Cohesins mutated in the Hinge or Loop1 regions of Smc1 bind chromatin by a mechanism similar to wild-type cohesin, but fail to enrich at cohesin-associated regions (CARs) and pericentric regions. Hence, the Hinge and Loop1 regions of Smc1 are essential for the specific chromatin binding of cohesin. This specific binding and a subsequent Ctf7/Eco1-dependent step are both required for the establishment of cohesion. We propose that a cohesin or cohesin oligomer tethers the Sister Chromatids through two chromatin-binding events that are regulated spatially by CAR binding and temporally by Ctf7 activation, to ensure cohesins crosslink only Sister Chromatids.
