Characterization of translation systems in vitro from three developmental stages of Strongylocentrotus purpuratus

Abstract

We have developed and characterized cell-free systems active in translation from unfertilized eggs, 30-min zygotes and hatched blastulae of the sea urchin Strongylocentrotus purpuratus. The ion concentrations selected for preparation of the lysates were 150 mM-K+, 40 mM-Na+, 40 mM-Cl-, 5 x 10(-7) M free Ca2+ and 1 mM free Mg2+. It was necessary to include the ribonuclease inhibitor RNas in the preparations to obtain full activity consistently. The pH optimum was 7.2 and was extremely sharp for the three S. purpuratus lysates. The temperature optima of the three lysates were remarkably similar to those of the intact unfertilized egg and embryos. Lysates from unfertilized egg and 30-min zygotes showed a temperature optimum at 15 degrees C. The hatched blastula lysate showed a broader temperature optimum with a shift to about 20 degrees C. The optimized lysates incorporated radiolabelled amino acids into polypeptides for up to 90 min. The polypeptides synthesized ranged in Mr from 200,000 to 20,000, suggesting that the mRNA in the lysates was intact and capable of directing the synthesis of complete polypeptides. Furthermore, the three lysates were capable of initiation, as demonstrated by inhibition of initiation using the inhibitors edeine and 7-methylguanosine 5′-triphosphate (m7GTP). At 15 degrees C, the transit times for the three lysates were: unfertilized egg, 40 min; 30-min zygotes and hatched blastula lysates, 20 min. These transit times are similar to those of intact eggs and embryos, and significantly, reflect the two-fold increase in elongation rate seen following fertilization in intact embryos. Thus, these lysates display many features and characteristic responses typical of intact eggs and embryos, indicating that the lysates should be useful tools for the analysis of translation control in early embryogenesis.