DNA sequence of human 5-HT2 receptor cDNA and deduced amino acid sequence of the human (H), rat (R), and mouse (M) 5-HT2 receptors. The seven proposed transmembrane domains are bracketed. Intron–exon junctions are indicated by arrows, and exons are labeled E1, E2, and E3. Amino acids in rat or mouse receptors that are different than those in the human are shown—as opposed to identical residue, which are designated with dots.