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J. Cell Biol.,
Volume 139, Number 4, November 17, 1997 975-983
European Molecular Biology Laboratory, Cell Biology Programme, D-69117 Heidelberg, Germany
To understand the role of microtubule-associated proteins (MAPs) in the regulation of microtubule (MT) dynamics we have characterized MAPs prepared from Xenopus laevis eggs (Andersen, S.S.L., B. Buendia, J.E. Domínguez, A. Sawyer, and E. Karsenti.
1994. J. Cell Biol. 127:1289-1299). Here we report on
the purification and characterization of a 310-kD MAP
(XMAP310) that localizes to the nucleus in interphase and to mitotic spindle MTs in mitosis. XMAP310 is
present in eggs, oocytes, a Xenopus tissue culture cell
line, testis, and brain. We have purified XMAP310 to
homogeneity from egg extracts. The purified protein
cross-links pure MTs. Analysis of the effect of this
protein on MT dynamics by time-lapse video microscopy has shown that it increases the rescue frequency
5-10-fold and decreases the shrinkage rate twofold. It
has no effect on the growth rate or the catastrophe frequency. Microsequencing data suggest that XMAP230
and XMAP310 are novel MAPs. Although the three
Xenopus MAPs characterized so far, XMAP215
(Vasquez, R.J., D.L. Gard, and L. Cassimeris. 1994. J. Cell Biol. 127:985-993), XMAP230, and XMAP310 are
localized to the mitotic spindle, they have distinct effects on MT dynamics. While XMAP215 promotes
rapid MT growth, XMAP230 decreases the catastrophe
frequency and XMAP310 increases the rescue frequency. This may have important implications for the
regulation of MT dynamics during spindle morphogenesis and chromosome segregation.
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