CHARACTERIZATION OF A 100-KDA HEAT-STABLE MICROTUBULE-ASSOCIATED PROTEIN FROM HIGHER-PLANTS

In higher-plant cells, the different cell-cycle-dependent microtubule arrays are involved in a wide range of activities including chromosome segregation, cell-plate formation and cellulose microfibril distribut ion and orientation. A wealth of data, obtained using animal cells, ha s indicated that the differential stability and function of microtubul es during cell-cycle and/or differentiation could be primarily regulat ed by selective microtubule-associated proteins (MAP). Compared to ani mal MAP, our knowledge of plant MAP is so far very limited. In this st udy, we have identified a maize heat-stable protein with apparent mole cular mass 100 kDa (P-100) which binds to taxol-stabilized neurotubule s and copolymerizes in vitro with purified neural tubulin. Moreover, P -100 cross-reacts with affinity-purified tau antibodies like a maize 8 3-kDa putative MAP described previously [Vantard, M., Schellenbaum, P. , Fellous, A. and Lambert, A. M. (1991) Biochemistry 30, 9334-9340]. P olyclonal antibodies directed against P-100 were obtained and indicate d that this protein is found in diverse higher-plant cultured cells su ggesting the ubiquitous nature of this protein. P-100 can be phosphory lated in vitro by protein kinases present in a maize cytosol extract. Together, our data suggest that P-100 could be a higher plant MAP.