Download - G2/M: Chromosome condensation
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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
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Cohesion and condensation
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Cohesins and condensins
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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
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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
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Condensin, histone H3 and the cell cycle
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Mitosis: Overview
Stages Prometaphase, metaphase, anaphase,
telophase Purpose: equational and equal
segregation of chromatids to daughter cells
Checkpoints
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Mitosis: Overview
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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
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The mitotic spindle
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The centromere and kinetochore
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The centromere and kinetochore
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MT dynamic instability
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Mitosis: Metaphase
Stable bipolar orientation achieved Role of tension
• Cohesin Tension-sensitive checkpoint
Anaphase signal
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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
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Synthesis - Destruction Cycle
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Cohesion release at M/A
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Control of anaphase entry
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Mitosis: Anaphase
Anaphase A - separation of chromosomes Mechanisms Where is the motor?
• Class, 04.23.02
Anaphase B - elongation of spindle
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Anaphase B