Fig. 1. (A) Primary structure of the urea transporter (UT) isolated from the kidney of the red-eared slider turtle, Trachemys scripta elegans. The deduced amino acid sequence is aligned with those of rat UT-A2 (U09957) and rat UT-B2 (U81518) using the Clustal algorithm. Asterisks denote identical amino acid residues to turtle UT. The horizontal bars indicate the predicted transmembrane regions. The box indicates putative N-glycosylation sites (NIT). The ALE domain, which is considered to be a signature sequence for the UT-B, is underlined. (B) Kyte–Doolittle hydropathy profile of the deduced Turtle UT amino acid sequence predicts the presence of transmembrane regions (1–10). (C) Phylogenetic tree showing the relationship between vertebrate UTs. The tree was constructed by the neighbor-joining method using ClustalW based on UT sequences. Numbers at branch points are derived from bootstrap analysis (1000 repetitions). UTs of bacteria, Desulfovibrio and Ochrobactrum, were regarded as outgroups. Scale bar represents a phylogenetic distance of 0.1 amino acid substitutions per site. The position of turtle UT is boxed. Each sequence appears in the protein database with the following accession nos: Desulfovibrio UT,YP-010379; Ochrobactrum UT, YP-001370983; fugu (pufferfish) UT-C, NP001033079; eel UT-C, BAD66672; human UT-B, AAH50539; mouse UT-B, AAI00571; rat UT-B, EDL84685; Triakis UT, BAC75980; stingray UT, AAQ23382; eel eUT, BAC53976; toadfish UT, AAD53976; tilapia UT, AAG49891; fugu UT, NP001027896; toad UT, BAF16706; frog UT, CAA73322; turtle UT, AB308450; rat UT-A2, AAA84392; whale UT-A2, BAF46914; and human UT-A2, CAA65657.