Talk:Cohesin

Interpretation of reference and explanation of findings is fundamentally incorrect

The article states:

"It is not clear how the cohesin ring links sister chromatids together. There are two possible scenarios:

1. Cohesin subunits bind to each sister chromatid and form a bridge between the two.
2. Since cohesin has a ring structure, it is able to encircle both sister chromatids.

Current evidence suggests that the second scenario is the most likely. Proteins that are essential for sister chromatid cohesion, such as Smc3 and Scc1, do not regulate the formation of covalent bonds between cohesin and DNA, indicating that DNA interaction is not sufficient for cohesion.[3] In addition, disturbing the ring structure of cohesin through cleavage of Smc3 or Scc1 triggers premature sister chromatid segregation in vivo.[9] This shows that the ring structure is important for cohesin’s function."

In fact, the Cell paper linked does not discuss the hypothesis that cohesin bind each chromatid and tether them together, and thus the reference does not prove that Smc3 and Scc1 don't bind cohesin to DNA. Additionally, the way this is written suggests that hypothesis #1 means that cohesin covalently bonds to the chromatids, which is both inaccurate and a misunderstanding of how proteins generally bind to DNA through intermolecular interactions, not chemical bonds.

The paper does address the second half of the paragraph. It essentially shows that cleaving Scc1 and Smc3 or disrupting Smc3's coiled coil domain results in cohesin's dissociation from chromatin, but does not interfere with subunit binding. This indicates that the cuts/modifications do not destabilize the complex, but they do break the supposed ring structure and allow the complex to be released. They show that this causes a deficiency in sister chromatid cohesion in vivo, although they don't take that much further. — Preceding unsigned comment added by 71.192.102.252 (talk) 21:58, 13 July 2019 (UTC)