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G2/M: Chromosome condensation

G2/M: Chromosome condensation. SMC family of proteins s tructural m aintenance of c hromosomes large coiled coil proteins with ATPase domain interact in complexes Cohesin - maintains sister-chromatid cohesion Condensin - mitotic chromosome condensation. Cohesion and condensation.

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G2/M: Chromosome condensation

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  1. G2/M: Chromosome condensation • SMC family of proteins • structural maintenance of chromosomes • large coiled coil proteins with ATPase domain • interact in complexes • Cohesin - maintains sister-chromatid cohesion • Condensin - mitotic chromosome condensation

  2. Cohesion and condensation

  3. Cohesins and condensins

  4. 13S Condensin • SMC2 and SMC4, with xCAP-D2, xCAP-G, xCAP-H (Drosophila barren) • 13S condensin induces positive writhe and supercoiling in DNA • Association of 13S with chromosomes occurs exclusively in mitosis • 13S in mitotic extracts: binds DNA, is phosphorylated, induces supercoil in presence of ATP and TOP1 • 13S in interphase extracts: binds DNA, is not phosphorylated, does not induce supercoil • Immunodepletion of cdc2 decreases P of 13S and leads to loss of condensin activity; adding cdc2 back increases P of 13S in condensin activity

  5. Histone H3 phosphorylation • An initiating event of chromosome condensation is phosphorylation of histone H3 on ser-10 • When site is mutated in Tetrahymena, there is aberrant chromosome condensation and segregation defects (but not in budding yeast!) • H3 Kinase? Not MPF, may be NIMA, or aurora kinase • RNAi depletion of aurora B decreases P of H3, decreases chromosome condensation, and leads to failure to recruit barren

  6. Condensin, histone H3 and the cell cycle

  7. Mitosis: Overview • Stages • Prometaphase, metaphase, anaphase, telophase • Purpose: equational and equal segregation of chromatids to daughter cells • Checkpoints

  8. Mitosis: Overview

  9. Mitosis: Prometaphase • Spindle morphogenesis • MTs, MT polarity and dynamic instability • MT motors • kinesin (+ end directed) • dynein (- end directed) • Centrosome and spindle assembly • Centromeres and kinetochores • “Dance” of the chromosomes • Bipolar orientation & importance

  10. The mitotic spindle

  11. The centromere and kinetochore

  12. The centromere and kinetochore

  13. MT dynamic instability

  14. Mitosis: Metaphase • Stable bipolar orientation achieved • Role of tension • Cohesin • Tension-sensitive checkpoint • Anaphase signal

  15. How do cells get out of metaphase? • Via anaphase by action of the anaphase promoting complex (APC) • Injection into Xenopus oocytes of RNA encoding non-degradable cyclin B leads to sustained high MPF and metaphase arrest • Ubiquitination of chromosome cohesins and cyclin targets them to the proteasome

  16. Synthesis - Destruction Cycle

  17. Cohesion release at M/A

  18. Control of anaphase entry

  19. Mitosis: Anaphase • Anaphase A - separation of chromosomes • Mechanisms • Where is the motor? • Class, 04.23.02 • Anaphase B - elongation of spindle

  20. Anaphase B

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