The kinetochore stretching is essential to silence the SAC. (A) A model illustrating the kinetochore stretching and the SAC silencing. Biorientation induces stretching of centromeres (modeled as a spring). Normally the kinetochores (yellow amorphous structures) undergo stretching, as denoted by arrows, and this kinetochore stretching promotes SAC inactivation. If kinetochore stretching is inhibited (e.g., by low nocodazole treatment or by condensin I depletion), SAC is maintained. (B) Proximal and distal kinetochores of monooriented chromosomes (top) were assessed for microtubule attachments by Mad2 recruitment as in Fig. 2 A (bottom). Monooriented chromosomes are indicated by arrowheads. (C) Stretching is induced at proximal but not at distal kinetochores of monooriented chromosomes. Profiles of the intra- and interkinetochore lengths and distances were assessed with the threshold values defined in Fig. 1 B (red dotted lines). The incidences for the kinetochore stretching were 13.2% and 0.0%, and the interkinetochore distances were 0.51 ± 0.02 µm (mean ± SEM) and 0.54 ± 0.02 µm for proximal (n = 38, 24 cells) and distal (n = 39, 24 cells) kinetochores, respectively. Bar, 5 µm.