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Curr Biol. 2008 Nov 11;18(21):1713-7. doi: 10.1016/j.cub.2008.09.046. Epub 2008 Oct 30.

Microtubule-driven multimerization recruits ase1p onto overlapping microtubules.

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Department of Physics and Astronomy, VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.


Microtubule (MT) crosslinking proteins of the ase1p/PRC1/Map65 family play a major role in the construction of MT networks such as the mitotic spindle. Most homologs in this family have been shown to localize with a remarkable specificity to sets of MTs that overlap with an antiparallel relative orientation [1-4]. Regulatory proteins bind to ase1p/PRC1/Map65 and appear to use the localization to set up precise spatial signals [5-10]. Here, we present evidence for a mechanism of localized protein multimerization underlying the specific targeting of ase1p, the fision yeast homolog. In controlled in vitro experiments, dimers of ase1-GFP diffused along the surface of single MTs and, at concentrations above a certain threshold, assembled into static multimeric structures. We observed that this threshold was significantly lower on overlapping MTs. We also observed diffusion and multimerization of ase1-GFP on MTs inside living cells, suggesting that a multimerization-driven localization mechanism is relevant in vivo. The domains responsible for MT binding and multimerization were identified via a series of ase1p truncations. Our findings show that cells use a finely tuned cooperative localization mechanism that exploits differences in the geometry and concentration of ase1p binding sites along single and overlapping MTs.

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