Membrane associated poly (A)-containing ribonucleoproteins in Artemia Salina gastrula embryos

Abstract

The embryonic development of Artemia salina is often interrupted by a period of dormancy at the gastrula stage. Although no endogeneous protein synthesis could be detected in these encysted embryos [ 11, the presence of stored mRNA has been demonstrated [2-4]. Messenger activity is associated with both poly(A)+-RNA and poly(A)--RNA extracted from the membrane fraction but only with the poly(A)-RNA of the free cytoplasmic ribonucleoproteins [3]. Poly(A)*-RNA of the cytoplasmic RNP is complexed with a translational inhibitor RNA, and messenger activity is restored if the inhibitor RNA is dissociated from the mRNA by the use of EDTA during the fractionation procedure [ 51. We have shown by sucrose gradient centrifugation that free cytoplasmic poly(A)+RNPs exhibited a heterogeneous distribution consisting of several discrete peaks ranging from 20-120 S [4]. Approximately 50% of the RNPs sedimented faster than 50 S and were complexed with ribosomes or ribosomal subunits. The presence of EDTA converted all these poly(A)*-RNPs into free 20-40 S particles. We demonstrate here that the poly(A)‘-RNPs of the membrane fraction exhibit a different size distribution on sucrose gradients as compared with the