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Fridman, Vladimir (2)
Gerson-Gurwitz, Adina (2)
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Hoyt, M. Andrew (1)
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Regulation of bi-directional movement of single kinesin-5 Cin8 molecules
Schmidt, Christoph F.
Kinesin-5 mechanoenzymes drive mitotic spindle dynamics as slow, processive microtubule (MT)-plus-end directed motors. Surprisingly, the Saccharomyces cerevisiae kinesin-5 Cin8 was recently found to be bi-directional: it can move processively in both directions on MTs. Two hypotheses have been suggested for the mechanism of the directionality switch: (1) single molecules of Cin8 are intrinsically minus-end directed, but mechanical coupling between two or more motors triggers the switch; (2) a single motor can switch direction, and “cargo binding” i.e., binding between two MTs triggers the switch to plus-end motility. Single-molecule fluorescence data we published recently, and augment here, favor hypothesis (2). In low-ionic-strength conditions, single molecules of Cin8 move in both minus- and plus-end directions. Fluorescence photo bleaching data rule out aggregation of Cin8 while they move in the plus and in the minus direction. The evidence thus points toward cargo regulation of directionality, which is likely to be related to cargo regulation in other kinesins. The molecular mechanisms of this regulation, however, remain to be elucidated.
Saccharomyces cerevisiae Cin8; kinesin directionality; kinesin-5; microtubules; mitosis
Phospho-regulation of kinesin-5 during anaphase spindle elongation
Hoyt, M. Andrew
Journal of Cell Science
The kinesin-5 Saccharomyces cerevisiae homologue Cin8 is shown here to be differentially phosphorylated during late anaphase at Cdk1-specific sites located in its motor domain. Wild-type Cin8 binds to the early-anaphase spindles and detaches from the spindles at late anaphase, whereas the phosphorylation-deficient Cin8-3A mutant protein remains attached to a larger region of the spindle and spindle poles for prolonged periods. This localization of Cin8-3A causes faster spindle elongation and longer anaphase spindles, which have aberrant morphology. By contrast, the phospho-mimic Cin8-3D mutant exhibits reduced binding to the spindles. In the absence of the kinesin-5 homologue Kip1, cells expressing Cin8-3D exhibit spindle assembly defects and are not viable at 37°C as a result of spindle collapse. We propose that dephosphorylation of Cin8 promotes its binding to the spindle microtubules before the onset of anaphase. In mid to late anaphase, phosphorylation of Cin8 causes its detachment from the spindles, which reduces the spindle elongation rate and aids in maintaining spindle morphology.
Cdk1; Cin8; Kinesin-5; Microtubules; Mitosis
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