Studies on a double-stranded RNA-binding zinc finger protein

Proteins containing C 2 H 2 type zinc finger motifs are perhaps the largest class of nucleic acid-binding proteins found in nature. This dissertation describes studies on a novel zinc finger protein, dsRBP-ZFa, isolated by screening a Xenopus cDNA expression library with dsRNA. The protein consists of a basic N-terminal region containing seven C 2 H 2 zinc finger motifs and an acidic C-terminal region that is not required for binding. The last four zinc finger motifs, and the linkers that join them, are nearly identical repeats, while the first three motifs and their linkers are each unique. I show that dsRBP-ZFa binds dsRNA and RNA-DNA hybrids with nanomolar dissociation constants and in a sequence independent manner. Additionally, ssRNA and DNA fail to compete for binding suggesting that dsRBP-ZFa prefers to bind an A-form helix. Studies using fragments of dsRBP-ZFa encompassing the three N-terminal, unique zinc finger motifs, and another encompassing the last three of the nearly identically motifs, show that these have binding properties similar to the full-length protein. I have conducted in situ mRNA hybridization experiments to investigate the expression pattern of dsRBP-ZFa mRNA in Xenopus embryos. These experiments revealed that dsRBP-ZFa mRNA is broadly expressed spatially and temporally within the Xenopus nervous system. Using western analyses, I also show that dsRBP-ZFa protein is primarily localized to the nucleus of stage 6 Xenopus oocytes and is present in Xenopus eggs. While other proteins have been shown to bind dsRNA, dsRBP-ZFa is the first example of a zinc finger protein with this activity. Possible biological roles for dsRBP-ZFa and experiments to elucidate these are discussed.