FIG. 2.

Comparison between the sequence of the human NaPi-3a protein (the human homologue of NaPi-2a; GenBank accession no. AAA36354) and the deduced sequence of the nptA gene product (GenBank accession no. CAA09443). (A) Alignment of deduced amino acid sequences. ∗, identity; +, conservative substitution; -, deletion or nonconservative substitution. Underlined sequences I to VIII represent predicted transmembrane helices in the eight-helix model proposed by Murer et al. (25), and HI to HIV represent additional predicted hydrophobic membrane-associated hinge regions (38). Corresponding predicted transmembrane helix regions are underlined in each sequence. (B) Schematic diagram of proposed NaPi-3a and NptA structures based on the transmembrane helix predictions shown in panel A (based on the model in reference 38). Note the deletion in the large extracellular loop and the absence of transmembrane helix VIII in NptA.