A novel 24-kDa microtubule-associated protein purified from sea urchin eggs

Chromatographic fractionation of a crude extract of sea urchin eggs on a hydrophobic column enabled us to find a new 24-kDa microtubule-associated protein (SU-MAP24) that bound tightly to the column and was eluted under alkaline conditions. Biochemical studies using the purified protein showed its direct binding to microtubules reconstituted from tubulin purified from starfish sperm outer fibers. SU-MAP24 promoted tubulin polymerization in a dose-dependent manner. Immunoblotting analysis showed that SU-MAP24 is present in a microtubule protein fraction obtained from a crude extract using taxol, and immunostaining of paraffin-sectioned metaphase eggs showed its localization in the mitotic apparatus. These results show that SU-MAP24 is a newly identified microtubule-associated protein.