A conserved triple arginine motif in OMA-1 is required for RNA-binding activity and embryo viability.

Sexually reproducing organisms make haploid gametes-oocytes and spermatocytes-that combine during fertilization to make an embryo. While both gametes contain similar DNA content, oocytes con-tain the bulk of the cytoplasm including maternally supplied mRNAs and proteins required prior to zygotic gene activation. RNA-binding proteins are key regulators of these maternal transcripts. In Caenorhabditis elegans, the tandem zinc finger proteins OMA-1 and OMA-2 are required for fertiliza-tion. Here, we show that OMA-1 RNA-binding activity requires a short basic region immediately up-stream from the canonical tandem zinc finger domain. Mutation of this region in animals produces a phenotype distinct from a genetic null. Oocytes can be fertilized, but fail to form an intact chitin egg-shell, frequently break in utero, and arrest prior to morphogenesis. Our results identify a critical region outside of the canonical RNA-binding domain required for both RNA-binding activity as well as re-vealing a new role for OMA-1 during the oocyte-to-embryo transition.