cohesion.txt

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Cohesion roles
- 1. Regulates SEPARATION of sister chromatids
- 2. Facilitates SPINDLE ATTACHMENT onto chromosomes
- 3. Facilitates DNA REPAIR
Mechanism for loading DNA
- ATP driven, cohesions need to Hydrolyze ATP (ATPase activity) to stabilize
- Cohesion loads onto DNA during G1 phase
- Scc 2/4 (Yeast) needed: RECRUITS cohesion near chromatin fibers
Cohesion structure
- V-shaped structure w/2 domains
- 1. ATPase activity domain
- 2. Hinge domain – allows for dimerization
Ring Model
- DNA is entrapped by Cohesion
- Does NOT BIND to DNA directly
- Hinge domain plays role in SISTER CHROMATID ENTRY
Ways of ring entrapment (3)
- 1. cohesion ring assembles around DNA: not plausible b/c cohesions exist as rings outside of chromatin
- 2. DNA broken and ring slides through
- 3. Ring OPENS and closes
Arguments against Ring model
- Localization of cohesion on genome not explained
- Cohesion will still be present on sister chromatids even after its not needed
- Lack of FLEXIBILITY of ring: 30nm chromatin fiber formation does not allow for ring
Handcuff Model
- Composed of 2 RINGS, dimerization
- Each ring surrounds one sister chromatid
- Rad21 bridges the two dimers (Smc3 and Smc1 of each dimer) Occurs during S phase (loading occurs during G1 phase)
Mechanism for Handcuff model
- Opening of each ring at Rad21 and Smc3 head to load onto DNA
- Ctf7/Eco1activate connection of 2 rings
Mechanism for Cleaving cohesin
- Cohesions removed prior to ANAPHASE
- Cleavage of Rad21/SA by PHOSPHORYLATION of S2: destabilizes complex and allows for DNA removal
- Separase prevents RE-Cohesion via REMOVAL of Rad21
Separase
- Activated by Anaphase promoting complex (APC)
- Acts on Scc1 component of Rad21 to promote cohesion REMOVAL

Author

rincrocci

150983

Card Set

cohesion.txt

Description

cohesion

Updated

2012-04-29T22:50:44Z

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