A XENOPUS ZINC-FINGER PROTEIN THAT SPECIFICALLY BINDS DSRNA AND RNA-DNA HYBRIDS

Proteins containing C2H2 type zinc finger motifs represent one of the largest classes of nucleic acid-binding proteins found in nature. We d escribe a novel zinc finger protein, dsRBP-ZFa, isolated by screening an expression library with dsRNA. The dsRBP-ZFa cDNA encodes a protein containing seven zinc finger motifs and an acidic C-terminal domain. Mobility shift experiments demonstrate that dsRBP-ZFa binds dsRNA and RNA-DNA hybrids with nanomolar dissociation constants and in a sequenc e independent manner. We also show that DNA and single stranded RNA fa il to compete with dsRNA for binding suggesting dsRBP-ZFa prefers to b ind an A-form helix. Using western analyses we have localized dsRBP-ZF a primarily to the nucleus of Xenopus laevis oocytes. The identificati on of dsRBP-ZFa provides the first example of a zinc finger protein th at is specific for dsRNA. In addition, dsRBP-ZFa does not contain the previously described dsRNA binding motif, suggesting certain zinc fing ers may provide an alternative way to recognize the A-form helix. (C) 1997 Academic Press Limited.