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Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599-3280
Activation of a facultative, dicentric chromosome provides a unique opportunity to introduce a
double strand DNA break into a chromosome at mitosis. Time lapse video enhanced-differential interference
contrast analysis of the cellular response upon dicentric activation reveals that the majority of cells initiates
anaphase B, characterized by pole-pole separation,
and pauses in mid-anaphase for 30-120 min with spindles spanning the neck of the bud before completing
spindle elongation and cytokinesis. The length of the spindle at the delay point (3-4 µm) is not dependent on
the physical distance between the two centromeres, indicating that the arrest represents surveillance of a dicentric induced aberration. No mid-anaphase delay is
observed in the absence of the RAD9 checkpoint gene,
which prevents cell cycle progression in the presence of damaged DNA. These observations reveal RAD9-
dependent events well past the G2/M boundary and
have considerable implications in understanding how
chromosome integrity and the position and state of the
mitotic spindle are monitored before cytokinesis.
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