Preferential synthesis of actin during early development of the slime mold Dictyostelium discoideum

The changes in protein synthesis during differentiation of the cellular slime mold Dictyostelium were studied by SDS-polyacrylamide gel electrophoresis. Total cell protein was analyzed following a 2-hr pulse-label. It was found that during the preaggregation stage, comprising the first third of the developmental cycle, a single major band accounts for more than 20% of the total labeled protein on the gel. This species was produced in at least 5–10-fold lower amounts, relative to total cell protein synthesis, in vegetative cells and in later developing stages. Actin was purified from vegetative cells and was found to correspond to the major band in several respects. The discovery of a single protein being synthesized in such quantity at a specific developmental stage provides a powerful tool for the isolation of a specific messenger RNA molecule and for an intensive study of all the factors involved in regulating protein synthesis in a eukaryotic organism.