title: Kinesin-5 Kip1 is a bi-directional motor that stabilizes microtubules and tracks their plus-ends in vivo.
abstract: In this study, we examined the anaphase functions of the S. cerevisiae kinesin-5 homolog Kip1. We show that Kip1 is attached to the mitotic spindle midzone during late anaphase. This attachment is essential to stabilize interpolar microtubule (iMTs) plus-ends. By detailed examination of iMT dynamics we show that at the end of anaphase, iMTs depolymerize in two stages: during the first stage, one pair of anti-parallel iMTs depolymerizes at a velocity of 7.7 µm/minute; during the second stage, ∼90 seconds later, the remaining pair of iMTs depolymerizes at a slower velocity of 5.4 µm/minute. We show that upon the second depolymerization stage, which coincides with spindle breakdown, Kip1 follows the plus-ends of depolymerizing iMTs and translocates toward the spindle poles. This movement is independent of mitotic microtubule motor proteins or the major plus-end binding or tracking proteins. In addition, we show that Kip1 processively tracks the plus-ends of growing and shrinking MTs, both inside and outside the nucleus. The plus-end tracking activity of Kip1 requires its catalytic motor function, because a rigor mutant of Kip1 does not exhibit this activity. Finally, we show that Kip1 is a bi-directional motor: in vitro, at high ionic strength conditions, single Kip1 molecules move processively in the minus-end direction of the MTs, whereas in a multi-motor gliding assay, Kip1 is plus-end directed. The bi-directionality and plus-end tracking activity of Kip1, properties revealed here for the first time, allow Kip1 to perform its multiple functions in mitotic spindle dynamics and to partition the 2-micron plasmid.
authors.affiliation: Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Fridman
authors.forename: Adina
authors.initials: A
authors.lastname: Gerson-Gurwitz
authors.forename: Ofer
authors.initials: O
authors.lastname: Shapira
authors.forename: Natalia
authors.initials: N
authors.lastname: Movshovich
authors.forename: Stefan
authors.initials: S
authors.lastname: Lakämper
authors.forename: Christoph F
authors.initials: CF
authors.lastname: Schmidt
authors.forename: Larisa
authors.initials: L
authors.lastname: Gheber
mesh_terms: D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D016547:Kinesins / Q000235:genetics* / Q000378:metabolism; D008868:Microtubule Proteins / Q000235:genetics / Q000378:metabolism; D008870:Microtubules / Q000235:genetics / Q000378:metabolism*; D008938:Mitosis; D018809:Proliferating Cell Nuclear Antigen / Q000235:genetics* / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D008868:Microtubule Proteins; D018809:Proliferating Cell Nuclear Antigen; D029701:Saccharomyces cerevisiae Proteins; C413374:p27 antigen; D016547:Kinesins
keywords: Anaphase B; Kinesin-5; Kip1; Microtubules; Mitosis