Activation of amino acids during sea urchin development

Abstract

Previous work from this laboratory has demonstrated that unfertilized sea urchin eggs have very little, if any, ability to incorporate in vivo labelled amino acids into their proteins. Incorporation begins immediately following fertilization but its rate becomes especially high between blastula and midgastrula (1, 10, 12). Experiments carried out in vitro (4, 5) indicate that the ribosomes isolated from unfertilized eggs are unable to incorporate amino acids into proteins but acquire this ability within 30 minutes after fertilization. However, the ribosomes from unfertilized eggs can be induced in vitro to synthesize polyphenylalanine by the addition of synthetic polyuridylic acid (13, 16, 17). These results seem, therefore, to warrant the suggestion that the lack of synthetic ability on the part of the ribosomes of the unfertilized egg may depend on the nonavailability of messenger RNA. That a new synthesis of RNA begins shortly after fertilization is indicated by the recent work of Gross and Cousineau (2). Another important step, and indeed the first one, in the process of protein synthesis to which, in the case of the sea urchin embryo, almost no attention has thus far been paid is the activation of amino acids.