During oogenesis and maturation of the sea urchin egg, large stores of mRNA are accumulated for subsequent use during early embryogenesis. Utilization of stored maternal mRNA occurs at a very low rate prior to fertilization. After fertilization, dramatic changes in mRNA availability and recruitment occur, allowing rapid increases in the synthetic rate of many proteins during early cleavage. Changes have been documented in both overall rates of maternal mRNA utilization and in the selection of particular mRNA species at different developmental stages. Our previous studies have allowed the development of cell-free translation systems from eggs and embryos that reproduce the overall differences observed in the intact system. This investigation proposes to utilize these cell-free systems, in conjunction with other approaches, to identify the cellular components involved in the utilization of maternal mRNA. Using the cell-free systems an inhibitor of eIF-4F activity has been discovered in the unfertilized egg, that decreases gradually in activity over the first 2-3 hr after fertilization. The identity and nature of the eIF-4F inhibitory activity will be characterized. The mechanism by which this activity inhibits the initiation sequence will also be investigated. The manner in which the inhibitor is inactivated after fertilization will be explored. To complement these studies, a systematic search for developmentally regulated mRNA-interactive proteins will be undertaken, using a protein blotting and in vitro binding technique, with capped 32p-labelled mRNA's synthesized in vitro.
