Changes in Ribosome-associated Proteins during Sea Urchin Development

Ribosomes isolated from unfertilised eggs of the sea urchin, Strongylocentrotus purpuratus, have a higher protein: RNA ratio than ribosomes extracted from blastula stage ribosomes. Approximately 64 additional protein equivalents are found per ribosome. Most of the proteins are of high molecular weight and are tightly bound, being resistant to high-salt and EDTA treatment. The majority of the proteins appear to be basic in nature and remain associated with the 40S subunit on dissociation of the ribosomes. The possible physiological significance of the additional proteins is discussed in terms of the activation of protein synthesis following fertilisation. Sea urchin ribosomes, isolated from various stages of development, showed differential protein-labelling patterns. The high molecular-weight proteins had preferentially higher specific activities and one ribosomal protein was particularly highly labelled, reaching a maximum at the gastrula stage of development. The functional role of this highly labelled protein during development is discussed.