Armadillo <p>The armadillo (Arm) repeat is an approximately 40 amino acid long tandemly repeated sequence motif first identified in the <taxon tax_id="7227">Drosophila melanogaster</taxon> segment polarity gene armadillo involved in signal transduction through wingless. Animal Arm-repeat proteins function in various processes, including intracellular signalling and cytoskeletal regulation, and include such proteins as beta-catenin, the junctional plaque protein plakoglobin, the adenomatous polyposis coli (APC) tumour suppressor protein, and the nuclear transport factor importin-alpha, amongst others [<cite idref="PUB00015440"/>]. A subset of these proteins is conserved across eukaryotic kingdoms. In higher plants, some Arm-repeat proteins function in intracellular signalling like their mammalian counterparts, while others have novel functions [<cite idref="PUB00015441"/>].</p><p>The 3-dimensional fold of an armadillo repeat is known from the crystal structure of beta-catenin, where the 12 repeats form a superhelix of alpha helices with three helices per unit [<cite idref="PUB00000951"/>]. The cylindrical structure features a positively charged grove, which presumably interacts with the acidic surfaces of the known interaction partners of beta-catenin.</p>