Subsets of the Zinc Finger Motifs in dsRBP-ZFa Can Bind Double-Stranded RNA

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Abstract
DsRBP-ZFa is a Xenopus zinc finger protein that binds dsRNA and RNA−DNA hybrids with high affinity and in a sequence-independent manner. The protein consists of a basic N-terminal region with seven C2H2 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. To identify which regions of the protein are involved in nucleic acid binding, we examined the ability of five protein fragments to bind dsRNA and RNA−DNA hybrids. Our studies reveal that a fragment encompassing the three N-terminal, unique zinc finger motifs and another encompassing the last three of the nearly identical motifs have binding properties similar to the full-length protein. Since these two fragments do not share zinc finger motifs of the same sequence, dsRBP-ZFa must contain more than one type of zinc finger motif capable of binding dsRNA. As with the full-length protein, ssRNA and DNA do not significantly compete for dsRNA binding by the fragments.