Multiple alignment of vertebrate DIO1 peptide sequences indicating conserved cysteines (red) and selenocysteine (blue). The alignment was performed with CLUSTAL W. * invariant amino acid. SwissProt identifiers correspond to the following species: Oreochromis niloticus (Nile tilapia), Fundulus heteroclitus (Atlantic killifish), Xenopus laevis (African clawed frog), Gallus gallus (domestic chicken), Suncus murinus (Asian house shrew), Rattus norvegicus (brown rat), Mus musculus (house mouse), Homo sapiens (human being), Heterocephalus glaber (naked mole-rat) (protein inferred from homology), Oryctolagus cuniculus (European rabbit), Sus scrofa (domestic pig), Phyllostomus discolor (pale spear-nosed bat) (protein inferred from homology), Felis catus (domestic cat), and Canis lupus familiaris (domestic dog).