Project description:Cohesin is a multisubunit complex that mediates sister-chromatid cohesion. Its Smc1 and Smc3 subunits possess ABC-like ATPases at one end of 50 nm long coiled coils. At the other ends are pseudosymmetrical hinge domains that interact to create V-shaped Smc1/Smc3 heterodimers. N- and C-terminal domains within cohesin's kleisin subunit Scc1 bind to Smc3 and Smc1 ATPase heads respectively, thereby creating a huge tripartite ring. It has been suggested that cohesin associates with chromosomes by trapping DNA within its ring. Opening of the ring due to cleavage of Scc1 by separase destroys sister-chromatid cohesion and triggers anaphase. We show that cohesin's hinges are not merely dimerization domains. They are essential for cohesin's association with chromosomes, which is blocked by artificially holding hinge domains together but not by preventing Scc1's dissociation from SMC ATPase heads. Our results suggest that entry of DNA into cohesin's ring requires transient dissociation of Smc1 and Smc3 hinge domains. Keywords: Cohesin loading, Scc1, Smc1, Smc3, Hinge opening, ChIP-chip
Project description:Cohesin stably holds together the sister chromatids from S phase until mitosis. To do so, cohesin must be protected against its cellular antagonist Wapl. Eco1 acetylates cohesinâs Smc3 subunit, which locks together the sister DNAs. We used yeast genetics to dissect how Wapl drives cohesin from chromatin and identified mutants of cohesin that are impaired in ATPase activity but remarkably confer robust cohesion that bypasses the need for the cohesin protectors Eco1 in yeast and Sororin in human cells. We uncover an unexpected functional asymmetry within the heart of cohesinâs highly conserved ABC-like ATPase machinery and show that an activity associated with one of cohesinâs two ATPase sites drives DNA release from cohesin rings. This key mechanism is conserved from yeast to humans. We propose that Eco1 locks cohesin rings around the sister chromatids by counteracting an asymmetric cohesin-associated ATPase activity. Effect of mutations in Smc1 and Smc3 on cohesin loading onto chromosomes
Project description:FACT mediates cohesin function on chromatin Cohesin is a key regulator of genome architecture with roles in sister chromatid cohesion and the organisation of higher-order structures during interphase and mitosis. The recruitment and mobility of cohesin complexes on DNA are restricted by nucleosomes. Here we show that cohesin role in chromosome organization requires the histone chaperone FACT. Depletion of FACT in metaphase cells affects cohesin stability on chromatin reducing its accumulation at pericentric regions and binding on chromosome arms. Using Hi-C, we show that cohesin-dependent TAD (Topological Associated Domains)-like structures in G1 and metaphase chromosomes are disrupted in the absence of FACT. Surprisingly, sister chromatid cohesion is intact in FACT-depleted cells, although chromosome segregation failure is observed. Our results uncover a role for FACT in genome organisation by facilitating cohesin dependent compartmentalization of chromosomes into loop domains.
Project description:Cohesin stably holds together the sister chromatids from S phase until mitosis. To do so, cohesin must be protected against its cellular antagonist Wapl. Eco1 acetylates cohesin’s Smc3 subunit, which locks together the sister DNAs. We used yeast genetics to dissect how Wapl drives cohesin from chromatin and identified mutants of cohesin that are impaired in ATPase activity but remarkably confer robust cohesion that bypasses the need for the cohesin protectors Eco1 in yeast and Sororin in human cells. We uncover an unexpected functional asymmetry within the heart of cohesin’s highly conserved ABC-like ATPase machinery and show that an activity associated with one of cohesin’s two ATPase sites drives DNA release from cohesin rings. This key mechanism is conserved from yeast to humans. We propose that Eco1 locks cohesin rings around the sister chromatids by counteracting an asymmetric cohesin-associated ATPase activity.
Project description:The ring-like cohesin complex plays an essential role in chromosome segregation, organization, and double-strand break repair through its ability to bring two DNA double helices together. Scc2 (NIPBL in humans) together with Scc4 function as the loader of cohesin onto chromosomes. Chromatin adapters such as the RSC complex facilitate localization of the Scc2-Scc4 cohesin loader. Here we identify a broad range of Scc2- chromatin protein interactions that are evolutionarily conserved and reveal a role for one complex, Mediator, in recruitment of the cohesin loader. We identified budding yeast Med14, a subunit of the Mediator complex, as a high copy suppressor of poor growth in Scc2 mutant strains. Physical and genetic interactions between Scc2 and Mediator are functionally substantiated in direct recruitment and cohesion assays. Depletion of Med14 results in defective sister chromatid cohesion and decreased binding of Scc2 at RNA Pol II transcribed genes. Previous work has suggested that Mediator, Nipbl, and cohesin connect enhancers and promoters of active mammalian genes. Our studies suggest an evolutionarily conserved fundamental role for Mediator in direct recruitment of Scc2 to RNA pol II transcribed genes. We identified two mutations in the evolutionarily conserved HEAT domain of SCC2 that result in significantly reduced growth, scc2R787G and scc2G1242V. This experiment uses ChIP Seq to examine global localization of Scc2 in the presence or absence of MED14.
Project description:Cohesin’s association with chromosomes is determined by loading dependent on the Scc2/4 complex and release due to Wapl. We show here that Scc2 also actively maintains cohesin on chromosomes during G1. It does so by blocking a Wapl-independent release reaction that requires opening the cohesin ring at its Smc3/Scc1 interface as well as the D loop of Smc1’s ATPase. The Wapl-independent release mechanism is switched off as cells activate Cdk1 and enter G2/M and cannot be turned back on without cohesin’s dissociation from chromosomes. The latter phenomenon enabled us to show that in the absence of release mechanisms, cohesin rings that have already captured DNA in a Scc2-dependent manner before replication no longer require Scc2 to capture sister DNAs during S phase.
Project description:The ring-like cohesin complex plays an essential role in chromosome segregation, organization, and double-strand break repair through its ability to bring two DNA double helices together. Scc2 (NIPBL in humans) together with Scc4 function as the loader of cohesin onto chromosomes. Chromatin adapters such as the RSC complex facilitate localization of the Scc2-Scc4 cohesin loader. Here we identify a broad range of Scc2- chromatin protein interactions that are evolutionarily conserved and reveal a role for one complex, Mediator, in recruitment of the cohesin loader. We identified budding yeast Med14, a subunit of the Mediator complex, as a high copy suppressor of poor growth in Scc2 mutant strains. Physical and genetic interactions between Scc2 and Mediator are functionally substantiated in direct recruitment and cohesion assays. Depletion of Med14 results in defective sister chromatid cohesion and decreased binding of Scc2 at RNA Pol II transcribed genes. Previous work has suggested that Mediator, Nipbl, and cohesin connect enhancers and promoters of active mammalian genes. Our studies suggest an evolutionarily conserved fundamental role for Mediator in direct recruitment of Scc2 to RNA pol II transcribed genes. We identified two mutations in the evolutionarily conserved HEAT domain of SCC2 that result in significantly reduced growth, scc2R787G and scc2G1242V. This experiment uses RNA-Seq analysis to study the effect of these mutations on gene expression.
Project description:The ring-like cohesin complex plays an essential role in chromosome segregation, organization, and double-strand break repair through its ability to bring two DNA double helices together. Scc2 (NIPBL in humans) together with Scc4 function as the loader of cohesin onto chromosomes. Chromatin adapters such as the RSC complex facilitate localization of the Scc2-Scc4 cohesin loader. Here we identify a broad range of Scc2- chromatin protein interactions that are evolutionarily conserved and reveal a role for one complex, Mediator, in recruitment of the cohesin loader. We identified budding yeast Med14, a subunit of the Mediator complex, as a high copy suppressor of poor growth in Scc2 mutant strains. Physical and genetic interactions between Scc2 and Mediator are functionally substantiated in direct recruitment and cohesion assays. Depletion of Med14 results in defective sister chromatid cohesion and decreased binding of Scc2 at RNA Pol II transcribed genes. Previous work has suggested that Mediator, Nipbl, and cohesin connect enhancers and promoters of active mammalian genes. Our studies suggest an evolutionarily conserved fundamental role for Mediator in direct recruitment of Scc2 to RNA pol II transcribed genes. We identified two mutations in the evolutionarily conserved HEAT domain of SCC2 that result in significantly reduced growth, scc2R787G and scc2G1242V. This experiment uses RNA-Seq analysis to study the effect of these mutations on gene expression.
Project description:The ring-shaped cohesin complex is thought to fulfil its roles in sister chromatid cohesion, genome stability and gene regulation by topologically encircling DNAs. The ring is formed by two Structural Maintenance of Chromosome (SMC) subunits, whose ATPase heads are linked by a kleisin subunit. Additional components, including the Mis4Scc2/NIPL cohesin loader, engage the kleisin. We applied crosslinking mass spectrometry to characterize cohesion complex in two conditions: initial binding and gripping state.