During metazoan development, polarization of the body axes is of critical importance, as asymmetric cell division initiates cell specialization pathways. A family of conserved RNA-binding proteins characterized by CCCH-type tandem zinc finger (TZF) domains is required for axis polarization and cell type specification in the early embryo of C. elegans. A cascade of events essential to the oocyte- to-embryo transition is initiated by two members of this family, OMA-1/2. The process initiates with OMA-1/2 turnover and culminates with asymmetric segregation of cellular components to opposing poles of the embryo. Mutation of OMA-1/2 blocks oocyte maturation and prevents fertilization. We have observed that OMA-1 binds RNA with relatively low specificity in vitro, but regulates specific mRNAs in vivo. We have also determined that OMA-1 RNA binding is highly cooperative, a feature never before observed in a protein from the CCCH-type TZF family. Our goal is to investigate OMA- 1/2 activity from structure to phenotype. We will determine the molecular mechanism or RNA-binding cooperativity using NMR spectroscopy, computer simulations, and quantitative biochemistry. We will also define how RNA-binding cooperativity defines OMA-1 biological activity in worms. We will determine which mRNAs are regulated by OMA-1/2 in oocytes and of these mRNAs which are the most critical to reproduction. This research will lead to a new understanding of how the molecular properties of OMA-1 determine its function in reproductive biology in living animals.