Establishment of DNA-DNA Interactions by the Cohesin Ring
Yasuto Murayama, Catarina P. Samora, Yumiko Kurokawa, Hiroshi Iwasaki and Frank Uhlmann
CellPublished Online January 18, 2018 DOI:10.1016/j.cell.2017.12.021
Pressrelease (In Japanese only)
DNA, which encodes a blueprint of life, is a very long molecular thread and is packed into a cellular nuclear by forming the protein-DNA supramolecular complex called chromosome. During cell proliferation, chromosomes are doubled up by copying DNA molecules before equal segregation to two daughter cells. To achieve this process smoothly without any mistakes, chromosome contains several special molecular structures. One of such essential chromosomal structures is sister chromatid cohesion. Literally, this is a physical connection which is formed between two duplicated chromosomes. Without cohesion, cell fails to segregate chromosomes properly and this can result in plethora of abnormal events including cell death and cancers. Cohesin is the ring-shaped protein complex and is vital for establishment of sister chromatid cohesion. How cohesin achieves cohesion establishment is one of open questions in chromosome biology.
In the current study, Murayama and colleagues purified the fission yeast cohesin and reconstituted its DNA binding reaction in a test tube. This revealed cohesin topologically entraps DNA inside of its ring. Moreover, cohesin tethers two DNA strands by topological embrace. If DNA-cohesin-DNA tethering is formed between two replicated chromosomes, this can establish chromosome cohesions.
Cohesin is a member of Structural Maintenance of Chromosome (SMC) protein complex family. SMC complexes play vital roles in chromosome organizations. Deficiencies in the complexes have been reported to cause human diseases and malfunctions including developmental disorders, cancers and infertility. The current study provides the first molecular glimpse at how an SMC complex, cohesin, tethers DNA strands.
Figure: a model of establishment of sister chromatid cohesion by the cohesin ring.
Cohesin tethers two DNA strands by topological embrace. DNA-cohesin-DNA tethering can provide a molecular bridge to establish cohesion between the replicated sister chromatids.