IDENTIFICATION OF A MID-ANAPHASE CHECKPOINT IN BUDDING YEAST

Activation of a facultative, dicentric chromosome provides a unique op portunity 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 th at the majority of cells initiates anaphase B, characterized by pole-p ole separation, and pauses in mid-anaphase for 30-120 min with spindle s spanning the neck of the bud before completing spindle elongation an d cytokinesis. The length of the spindle at the delay point (3-4 mu m) is not dependent on the physical distance between the two centromeres , indicating that the arrest represents surveillance of a dicentric in duced 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 eve nts well past the G2/M boundary and have considerable implications in understanding how chromosome integrity and the position and state of t he mitotic spindle are monitored before cytokinesis.