Figure 5.

Proposed model for the physiological role of the bidirectional motility of fungi kinesin-5 motor proteins, adapted from [62]. (A) Prior to spindle assembly, the minus-end directed motility of bidirectional kinesin-5 motors causes their accumulation at the minus-ends of the MTs, near the SPBs. (B) At this stage, MTs from duplicated spindle poles come into antiparallel contact due to thermal pivoting, facilitated by flexible tether linking MT minus-ends and the SPB [235]. Kinesin-5 motors, accumulated in clusters near the SPBs, capture these antiparallel-oriented MTs, crosslink, and slide them apart via their plus-end directed motility. This plus-end directed motility is achieved by the clustering of kinesin-5 motors near the spindle poles and the binding to the two antiparallel MTs [62,148]. (C) The initial separation of the spindle poles, caused by the antiparallel sliding of MTs, generates additional MT overlap—which creates additional sites for the kinesin-5 motors to crosslink and slide apart antiparallel MTs. (D) Formation of the final bipolar spindle structure is achieved. The curved purple arrows indicate the direction of SPB movement during separation. Green arrows indicate the direction of motor motility.