Fig. 21-16

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Fig. 21-16
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Fig. 21-7
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Condensins Structural maintenance of chromosomes
(SMC) class of proteins. Very large, long coiled,
coil proteins with ATPase domains at each end.
Mutations in the condensins of budding yeast
interfere with proper chromosomal
segragation. When anti-bodies to the homologous
Xenopus condensins were used to deplete them from
an egg extract, the DNA of added sperm nuclei
replicated, but did not condense. Therefore,
condensins are required for chromosomal
condensation.
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Condensins become phosphorylated by MPF during
mitosis. In vitro, phosphorylated condensins
from mitotic extracts can supercoil DNA. But
dephosphorylated condensins following treatment
with a protein phosphatase.
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Fig. 4-7
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Fig. 21-18
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Fig. 21-18
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Fig. 21-18
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Degradation of Cyclin B is required for
chromosome decondensation and disassembly of the
spindal apparatus. But degradation of Cyclin B
is not required for chromosome separation
(anaphase).
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When Xenopus egg extracts were depleted of
cohesins using anti-cohesin antibodies bound to a
solid support, the depleted extracts replicated
sperm DNA, but the resulting sister chromatids
did not associate with each other
properly. Therefore cohesins are required for
sister chromosome association at the centromere.
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Fig. 20-33
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Fig. 21-19
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Securin
Cdc20
Cdh1
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Because Cdc20--the specificity factor that
directs APC to securin--is activated before Cdh1,
the specificity factor that directs the APC to
mitotic cyclins, MPF activity does not decrease
until after the chromosomes have
segragated. Consequently, chromosomes do not
decondense and the nuclear envelope does not
reassemble until the chromosomes have segragated.
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Prophase to Early Anaphase
MPF
Phosphatases
MPF substrate
Late Anaphase, Telophase and Interphase
P
Phosphatases
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Fig. 21-20
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Fig. 20-42
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Fig. 20-42