Translation of maternal messenger ribonucleoprotein particles from sea urchin in a cell-free system from unfertilized eggs and product analysis

Abstract

Maternal mRNP particles were isolated from the postribosomal supernatant fluid of unfertilized sea urchin eggs. They were translated in a cell-free system derived from unfertilized eggs. The translation of these particles required the presence of 12 m M MgCl 2, which is considered very high. The same high Mg 2+ requirement was observed when mRNP particles were translated in a cell-free system from morula embryos. In contrast, mRNA extracted from mRNP particles is translated at 3 m M MgCl 2. This concentration of Mg 2+ is known to be optimal for initiation of mRNA translation. Likewise, a rabbit globin mRNA is faithfully translated into α and β globin chains in a cell-free system from eggs at 3, but not at 12, m M MgCl 2. The translational products directed by mRNP or by mRNA derived from mRNP were examined in two gel systems and were found to be very similar. In both cases, histones were identified as part of the translational product. This indicated that the translation of mRNP in high Mg 2+ is not due to nonspecific binding of these particles to ribosomes. The rates of globin synthesis in a cell-free system derived from eggs is comparable to that of morula ribosomes and to that reported for translation of globin with mouse liver and reticulocyte ribosomes, indicating that unfertilized sea urchin egg ribosomes do not possess a translational inhibitor and that no deficiency in initiation factors for mRNA translation could explain the low rate of protein synthesis in unfertilized sea urchin eggs.