ABSTRACT
We have isolated a 70kD microtubule-binding protein from eggs of a starfish, Asterias amurensis, that promotes egg microtubule assembly in vitro (Hosoya et al., 1990). Using indirect immunofluorescence microscopy with the anti-70kD protein antiserum, the 70kD protein was localized on microtubule structures spread widely throughout the cytoplasm, the sperm aster, and the mitotic apparatus in starfish oocytes and eggs during both meiosis and mitosis. The sperm axonemes, however, were not detected by the antiserum. Immunoblot analysis showed that protein species immunologically related to the 70kD protein with different molecular masses as well as 70kD species are found in starfish neuronal tissues. The 70kD protein has a distinct binding site on microtubules from those of mammalian brain microtubule-associated proteins (MAPs); the binding of 70kD protein to brain microtubules was not inhibited by the presence of MAP2 or tau. The 70kD protein has several isoforms, suggesting the possibility of the posttranslational modification(s). The 70kD protein is a novel microtubule-binding protein and may be involved in the dynamic changes of microtubule structures in the cell.
