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Essential Roles of the Smc5/6 complex in Replication through Pausing Sites and Endogenous DNA Damage Tolerance

ABSTRACT: The essential functions of the conserved Smc5/6 complex remain elusive. To uncover its roles in genome maintenance, we established Saccharomyces cerevisiae cell cycle-regulated alleles that enable restriction of Smc5/6 components to S or G2/M. Unexpectedly, the essential functions of Smc5/6 segregated fully and selectively to G2/M. Genetic screens that became possible with generated alleles identified processes that crucially rely on Smc5/6 specifically in G2/M: metabolism of DNA recombination structures triggered by endogenous replication stress, and replication through natural pausing sites located in late-replicating regions. In the first process, Smc5/6 modulates remodeling of recombination intermediates, cooperating with dissolution activities. In the second, Smc5/6 prevents chromosome fragility and toxic recombination instigated by prolonged pausing and the fork protection complex, Tof1-Csm3. Our results thus dissect Smc5/6 essential roles, and reveal that combined defects in DNA damage tolerance and pausing site-replication cause recombination-mediated DNA lesions, which we propose to drive developmental and cancer-prone disorders.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE72241 | GEO | 2015/11/19

SECONDARY ACCESSION(S): PRJNA293458

REPOSITORIES: GEO

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Essential Roles of the Smc5/6 complex in Replication through Pausing Sites and Endogenous DNA Damage Tolerance

Project description:The essential functions of the conserved Smc5/6 complex remain elusive. To uncover its roles in genome maintenance, we established Saccharomyces cerevisiae cell cycle-regulated alleles that enable restriction of Smc5/6 components to S or G2/M. Unexpectedly, the essential functions of Smc5/6 segregated fully and selectively to G2/M. Genetic screens that became possible with generated alleles identified processes that crucially rely on Smc5/6 specifically in G2/M: metabolism of DNA recombination structures triggered by endogenous replication stress, and replication through natural pausing sites located in late-replicating regions. In the first process, Smc5/6 modulates remodeling of recombination intermediates, cooperating with dissolution activities. In the second, Smc5/6 prevents chromosome fragility and toxic recombination instigated by prolonged pausing and the fork protection complex, Tof1-Csm3. Our results thus dissect Smc5/6 essential roles, and reveal that combined defects in DNA damage tolerance and pausing site-replication cause recombination-mediated DNA lesions, which we propose to drive developmental and cancer-prone disorders. BrdU incorporation profiles by ssDNA-BrdU IP on chip have been generated as described (Katou et al., 2003). Protein binding profiles by ChIP-chip analysis were generated as described (Bermejo et al., 2009). Labeled probes were hybridized to Affymetrix S.cerevisiae Tiling 1.0 (P/N 900645) arrays and processed with TAS software.

2015-11-19 | E-GEOD-72241 | biostudies-arrayexpress

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Project description:Smc5/6 is essential for genome structural integrity by yet unknown mechanisms. Here we find that Smc5/6 co-localizes with the DNA crossed-strand processing complex Sgs1-Top3-Rmi1 (STR) at genomic regions known as natural pausing sites (NPSs) where it facilitates Top3 retention. Individual depletions of STR subunits and Smc5/6 cause similar accumulation of joint molecules (JMs) composed of reversed forks, double Holliday Junctions and hemicatenanes, indicative of Smc5/6 regulating Sgs1 and Top3 DNA processing activities. We isolate an intra-allelic suppressor of smc6-56 proficient in Top3 retention but affected in pathways that act complementarily with Sgs1 and Top3 to resolve JMs arising at replication termination. Upon replication stress, the smc6-56 suppressor requires STR and Mus81-Mms4 functions for recovery, but not Srs2 and Mph1 helicases that prevent maturation of recombination intermediates. Thus, Smc5/6 functions jointly with Top3 and STR to mediate replication completion and influences the function of other DNA crossed-strand processing enzymes at NPSs.

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Project description:Replication forks temporarily or terminally pause at hundreds of hard-to-replicate regions around the genome. A conserved pair of budding yeast replisome components Tof1-Csm3 (fission yeast Swi1-Swi3 and human TIMELESS-TIPIN) acts as a ‘molecular brake’ and promotes fork slowdown at proteinaceous replication fork barriers (RFBs), while the accessory helicase Rrm3 assists the replisome in removing protein obstacles. Here we show that Tof1-Csm3 complex promotes fork pausing independently of Rrm3 helicase by recruiting topoisomerase I (Top1) to the replisome. Topoisomerase II (Top2) partially compensates for the pausing decrease in cells when Top1 is lost from the replisome. The C-terminus of Tof1 is specifically required for Top1 recruitment to the replisome and fork pausing but not for DNA replication checkpoint (DRC) activation. We propose that forks pause at proteinaceous RFBs through a ‘sTOP’ mechanism (‘slowing down with TOPoisomerases I-II’), which we show also contributes to protecting cells from topoisomerase-blocking agents.

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Project description:During meiosis, Structural Maintenance of Chromosome (SMC) complexes underpin two fundamental features of meiosis: homologous recombination and chromosome segregation. While meiotic functions of the cohesin and condensin complexes have been delineated, the role of the third SMC complex, Smc5/6, remains enigmatic. Diminished Smc5/6 function causes severe defects in nuclear division, but the underlying causes of these defects remain unclear. Here we identify specific, essential meiotic functions for the Smc5/6 complex in homologous recombination and regulation of cohesin. We show that Smc5/6 is enriched at centromeres and cohesin-association sites where it regulates sister-chromatid cohesion and the timely removal of cohesin from chromosomal arms, respectively. Smc5/6 also localizes to recombination hotspots, where it promotes normal formation and resolution of joint-molecule intermediates. Furthermore, we find that Smc5/6 specifically promotes resolution of joint molecules via the XPF-family endonuclease, Mus81-Mms4Eme1. We propose that Smc5/6 acts as a chaperone for M-bM-^@M-^XmitoticM-bM-^@M-^Y-like recombination processes during meiosis. ChIP-chip was used to compare Smc5 localization in wild-type and spo11 strains

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Project description:DNA duplication is intimately connected to setting up post-replicative chromosome structures and events, but molecular details of this coordination are not well understood. A striking example occurs during yeast meiosis, where replication locally influences timing of the DNA double-strand breaks (DSBs) that initiate recombination. We show here that replication-DSB coordination is eliminated by overexpressing Dbf4-dependent Cdc7 kinase (DDK) or removing Tof1 or Csm3, components of the replication fork protection complex (FPC). DDK physically associates with Tof1, and Tof1 is dispensable for replication-DSB coordination if DDK is artificially tethered to replisomes. Furthermore, DDK phosphorylation of the DSB-promoting factor Mer2 is locally coordinated with replication, dependent on Tof1. These findings indicate that DDK recruited by FPC to replisomes phosphorylates chromatin-bound Mer2 in the wake of the replication fork, thus synchronizing replication with an early prerequisite for DSB formation. This may be a general mechanism to ensure spatial and temporal coordination of replication with other chromosomal processes.

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SMC5/6 facilitates joint molecule resolution and stepwise loss of cohesin to promote meiotic chromosome segregation

Project description:During meiosis, Structural Maintenance of Chromosome (SMC) complexes underpin two fundamental features of meiosis: homologous recombination and chromosome segregation. While meiotic functions of the cohesin and condensin complexes have been delineated, the role of the third SMC complex, Smc5/6, remains enigmatic. Diminished Smc5/6 function causes severe defects in nuclear division, but the underlying causes of these defects remain unclear. Here we identify specific, essential meiotic functions for the Smc5/6 complex in homologous recombination and regulation of cohesin. We show that Smc5/6 is enriched at centromeres and cohesin-association sites where it regulates sister-chromatid cohesion and the timely removal of cohesin from chromosomal arms, respectively. Smc5/6 also localizes to recombination hotspots, where it promotes normal formation and resolution of joint-molecule intermediates. Furthermore, we find that Smc5/6 specifically promotes resolution of joint molecules via the XPF-family endonuclease, Mus81-Mms4Eme1. We propose that Smc5/6 acts as a chaperone for ‘mitotic’-like recombination processes during meiosis.

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