Card Set Information

2012-04-29 18:50:44

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  1. Cohesion roles
    • 1. Regulates SEPARATION of sister chromatids
    • 2. Facilitates SPINDLE ATTACHMENT onto chromosomes
    • 3. Facilitates DNA REPAIR
  2. 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
  3. Cohesion structure
    • V-shaped structure w/2 domains
    • 1. ATPase activity domain
    • 2. Hinge domain – allows for dimerization
  4. Ring Model
    • DNA is entrapped by Cohesion
    • Does NOT BIND to DNA directly
    • Hinge domain plays role in SISTER CHROMATID ENTRY
  5. 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
  6. 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
  7. 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)
  8. Mechanism for Handcuff model
    • Opening of each ring at Rad21 and Smc3 head to load onto DNA
    • Ctf7/Eco1activate connection of 2 rings
  9. 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
  10. Separase
    • Activated by Anaphase promoting complex (APC)
    • Acts on Scc1 component of Rad21 to promote cohesion REMOVAL