Models for PEF-based modulation of error correction around spindle poles and sources of PEF production. (A) A model of PEF gradients across the metaphase spindle predicts that as a chromosome approaches a spindle pole it will experience progressively higher levels of PEF-mediated kt-MT stabilization because of elevated tension at kinetochores. (B) Model for generation of PEFs that oppose kinetochore-mediated pulling forces to create tension at kinetochores. We propose that chromosome-associated proteins with either plus end–directed motility or end tracking activity can generate PEFs.