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Professor Mark Sansom, Head of Department
Closing the cohesin ring round sister chromatids
Crystal structure of the Smc3 head with coiled coil section (Smc3hdCC) in complex with the N-terminal domain of kleisin (Scc1-N). The Smc1 head domain (Smc1hd) is shown in red in dimer formation with the Smc3 head (Click to enlarge)
A new study completes the structural and functional picture of the cohesin ring that traps DNA during mitosis until the critical moment of cell division.
The researchers behind the work, from Kim Nasmyth's lab in the department and the lab of Jan Löwe at the MRC LMB in Cambridge, describe their findings in a recent paper in Science (1).
Using the new structural information, the group has confirmed the presence of the tripartite cohesin ring in living cells and can begin to look at the mechanisms behind cohesin's functions.
Cohesin is a highly conserved complex comprised of subunits Smc1 and Smc3 forming a v-shaped conformation. These associate with a kleisin subunit to form what is believed to be a ring that holds sister chromatids together during mitosis until exactly the right time for their separation (2).
The interface between Smc3 and kleisin is a key regulatory one. Smc3 acetylation ensures that the ring is locked tightly shut, but release can be triggered by regulatory subunits that allow exit of the sister DNAs.
As Thomas Gligoris, one of the postdocs in the Nasmyth lab, explains, an understanding of this interface has so far eluded researchers. 'We had the crystal structure of the Smc1/Smc3 interface and also the Smc1/kleisin interface but were missing the structure of the Smc3/kleisin interface.'