Figure 8.

Models for histone depletion-induced SAC activation. At the pericentric chromatin, Top2 and condensin are responsible for the axial compaction of an intramolecular loop that provides the tensile properties of the centromere (A). Condensin/Top2-dependent alterations of the pericentric chromatin might affect the geometry of the sister kinetochores leading to syntelic attachments (B). An accumulation of torsional stress at the pericentric chromatin might also contribute to SAC activation by either altering the geometry of the sister kinetochores (C) or overly tightening the intramolecular loop (D). All situations would leave the kinetochores close to the inner centromere and thereby to Ipl1, which would destabilize the attachments and activate the SAC.