Uracil in DNA is usually considered to be an error, but it may be used for signaling in Drosophiladevelopment via recognition by a novel uracil-DNA-degrading factor (UDE) [(Bekesi Aet al. (2007) Biochem Biophys Res Commun355, 643–648]. The UDE protein has no detectable similarity to any other uracil-DNA-binding factors, and has no structurally or func-tionally described homologs.