Polyribosomal protein synthesis in fertilized sea urchin eggs: The effect of actinomycin treatment

Abstract

The protein synthesis initiated at fertilization in sea urchin eggs occurs, at least in part, on polyribosomes. Eggs treated with actinomycin D show a normal response to fertilization. The actinomycin-treated embryos suffer an 80–90% loss in the synthesis of new RNA with potential template function. In these cells, protein synthesis attains rates as high as those in controls. The actinomycin-resistant protein synthesis also occurs on polyribosomes, and on the basis of ribonuclease sensitivity, such units do not differ in any important way from those found in the normal early embryo. The unfertilized egg seems not to contain polyribosomes which are extracted by the methods used for embryos. These facts support the hypothesis that certain kinds of messenger RNA are present in the unfertilized egg, and that free ribosomes are unable to attach in a way that allows translation to take place.