Changes in glycerol solubility and amino acid incorporation of a protein possessing the characteristics of tubulin during first cleavage in the sea urchin embryo.

A method is described for the quantitation of the pool size of a tubulin like protein during synchronized cell division in the sea urchin Lytechinus variegatus. The method involves the use of a thin SDS slab polyacrylamide gel system in which tubulin can be quantitated in the submicrogram range. Employing a microtubule stabilization buffer, the intact tubule fraction was removed and the soluble tubulin pool was quantitated with this gel system. Amino acid incorporation into this protein was also quantitated. The resulting specific activity values and values for the amount of tubulin-like protein present in the pool fraction suggested that the tubulin pool decreases at fertilization and then remains constant through the first cell cycle. Tubulin synthesis, however, steadily increased after fertilization and then decreased dramatically just prior to mitotic apparatus formation. No change in tubulin pool size was observed at the time of peak mitotic appartus formation. These results are discussed in terms of the regulation of microtubule function.