Abstract
SummarySister chromatid cohesion conferred by entrapment of sister DNAs within a tripartite ring formed between cohesin’s Scc1, Smc1, and Smc3 subunits is created during S and destroyed at anaphase through Scc1 cleavage by separase. Cohesin’s association with chromosomes is controlled by opposing activities: loading by Scc2/4 complex and release by a separase-independent releasing activity as well as by cleavage. Coentrapment of sister DNAs at replication is accompanied by acetylation of Smc3 by Eco1, which blocks releasing activity and ensures that sisters remain connected. Because fusion of Smc3 to Scc1 prevents release and bypasses the requirement for Eco1, we suggested that release is mediated by disengagement of the Smc3/Scc1 interface. We show that mutations capable of bypassing Eco1 in Smc1, Smc3, Scc1, Wapl, Pds5, and Scc3 subunits reduce dissociation of N-terminal cleavage fragments of Scc1 (NScc1) from Smc3. This process involves interaction between Smc ATPase heads and is inhibited by Smc3 acetylation.
Highlights
Sister chromatid cohesion essential for chromosome segregation is mediated by a multisubunit complex called cohesin (Guacci et al, 1997; Michaelis et al, 1997), which contains two SMC proteins, Smc1 and Smc3, and an a-kleisin subunit Scc1
Sister chromatid cohesion is thought to be mediated by entrapment of sister DNAs within these rings (Haering et al, 2002), a concept known as the ring model
N-terminal cleavage fragments of Scc1 (NScc1) Is Stabilized by Releasing Activity Mutations We previously demonstrated that Smc3 is deacetylated by Hos1 in response to Scc1 cleavage at the onset of anaphase (Beckouet et al, 2010)
Summary
Sister chromatid cohesion essential for chromosome segregation is mediated by a multisubunit complex called cohesin (Guacci et al, 1997; Michaelis et al, 1997), which contains two SMC proteins, Smc and Smc, and an a-kleisin subunit Scc. Sister chromatid cohesion essential for chromosome segregation is mediated by a multisubunit complex called cohesin (Guacci et al, 1997; Michaelis et al, 1997), which contains two SMC proteins, Smc and Smc, and an a-kleisin subunit Scc1 Both Smc proteins form 50-nm-long intramolecular antiparallel coiled coils with a hinge/dimerization domain at one end and at the other an ATPase head domain formed from the protein’s N- and C-terminal sequences. Bacterial Smc/kleisin complexes form very similar tripartite rings (Burmann et al, 2013) that entrap DNAs (Wilhelm et al, 2015), raising the possibility that all Smc/ kleisin complexes operate as topological devices
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