Pairwise % identity of DNA and amino acid sequences was determined using the FASTA program from the PC GENE software. Genomic DNA regions comprising the entire coding sequence, the intron, and the promoter region were aligned. The 5′ flanking promoter region, which was analyzed contained the first 200 nucleotides preceding the putative transcription initiation site (Fig 1B). Amino acids from the entire coding region or from portions corresponding to the Leu-rich domain (LR), the region connecting the Leu-rich domain to the membrane (LR → TM), and the region comprising the transmembrane and intracellular domains (TM + IC) were aligned.