Polypeptides of nonpolyribosomal messenger ribonucleoprotein complexes of sea urchin eggs

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Abstract
RNA competent in directing protein synthesis is sequestered in unfertilized sea urchin eggs as translationally quiescent, nonpolyribosomal messenger ribonucleoprotein complexes (mRNP). Following fertilization these mRNP are derepressed and actively translated, presumably due to changes in the mRNA-associated proteins and their interaction with the mRNA. Poly(A)-containing egg mRNP free of contaminating monoribosomes and ribosomal subunits were isolated by chromatography on oligo(dT)-cellulose and identified their constituent proteins. Egg mRNP isolated by using near physiological ionic conditions have 15-20 major proteins, most of which are in the MW range of 40,000-100,000 and .apprx. 15-23 minor proteins in the 22,000-190,000 MW range. The association of the proteins with poly(A)-containing mRNA is indicated by their greatly reduced retention on oligo(dT)-cellulose after pretreatment of the crude mRNP fraction with saturating amounts of poly(uridylic acid). Three proteins present in poly(A)-containing mRNP from eggs, with MW of 48,000, 67,000 and 140,000, were not detected in poly(A)-containing mRNP derived from polyribosomes of hatched blastula-stage embryos. Stoichiometric differences were found between some of the proteins associated with the 2 types of mRNP. The potential regulatory role of these proteins is discussed.