PROTEIN SYNTHESIS AND THE MITOTIC APPARATUS.

Sea urchin eggs, exposed to a radioactive amino acid during the period from fertilization to metaphase of the first cleavage, incorporate the label into proteins. Some radioactivity is localized in the region of the mitotic apparatus (MA). The specific activity of proteins from isolated mitotic apparatus is more than three times that of the proteins from the rest of the cell, although under the conditions used for isolation only 11 percent of the total incorporated label is in the MA. The radio-activity is found in proteins that do not contribute significantly to the bulk of the MA protein, but this description might possibly apply to the fibrous skeleton. Electron microscope autoradiograms reveal a close association of radioactivity with the fibers.