Abstract
Newly synthesized proteins were pulse labeled with radioactive amino acids at several developmental stages of the sea urchin, Arbacia punctulata-in normal embryos and in embryos continuously exposed to the drug Dactinomycin. The soluble proteins were fractionated by electrophoresis through polyacrylamide gels. A simple procedure for complete solubilization of the proteins in slices of gels into a solution of toluene for liquid scintillation counting, and a computer program to display and to compare statistically the distributions of (14)C- and (3)H-labeled proteins fractionated on the same gel, allowed quantitative statements to be made on the relative changes in protein synthesis. The conclusion is that translation-level control provides most of the changes in protein synthesis that occur between fertilization and hatched blastula stage.