Figure 3.—

Genomic structure, predicted amino acid sequence, phylogenetic relationships, and muscle expression of ser-5. (A) New ser-5 genomic structure predicted from RACE. ser-5 contains eight exons and seven introns and exhibits an intron/exon pattern similar to that predicted for its C. briggsae homolog, CBG04044. Intron positions conserved in the human 5-HT6 receptor are indicated by a red line. (B) Predicted amino acid sequence and membrane-spanning model of SER-5. Amino acids potentially involved in ligand binding, G-protein coupling, sequestration, and desensitization are illustrated (Moro et al. 1993; Barak et al. 1994; Roth et al. 1997). Potential PKC, PKA, and palmitolylation sites were identified using Scanprosite. (C) Unrooted phylogenetic tree of previously characterized vertebrate and invertebrate 5-HT receptors. Sequences were modified to remove hypervariable regions by deletion of the N termini, 5 amino acids before the first predicted transmembrane domains; the third intracellular loops, 5 amino acids after and before predicted transmembrane domains 5 and 6, respectively; and the C termini, 10 amino acids following predicted transmembrane domain 7. Annotated sequences were initially aligned using MegAlign in DNAStar with Clustal W using default parameters and fine-tuned by hand. Bootstrapping was undertaken in DNAStar (1000 replicates with random seed). Homo sapiens (H): H5HT-1a (CAA40962), H5HT1b (P28222), H5HT1d (P28221), H5HT1e (CAA77558), H5HT1f (AAA36605), H5HT2a (CAA40963), H5HT2b (CAA54513), H5HT2c (AAF35842), H5HT4 (Q13639), H5HT5a (CAA57168), H5HT6 (AAA92622), Hs5HT7 (CAH69965). C. elegans (Ce) in red: CeSER1 (NP_001024728), CeSER4 (NP_497452), CeSER7 (NP_741730), and CeSER5 (our unpublished results). C. briggsae (Cb): CbSER-1 (CAE69959), CbSER4 (CAE69091), CbSER7 (CAE58847), and CbSER5 (CAE60436). Aedes egyptii (Ae): Ae5HT7 (AAG49292). Drosophila melanogaster (Dm): Dm5HT7 (NP_524599), Dm5HT2a (NP_725849), Dm5HT2b (CAA77571), and Dm5HT (NP_730859). Haemonchus contortus (Hc): Hc5HT1e (AAO45883). Ascaris suum (As): As5HT-2c (AAC78396). (D) Expression of a full-length ser-5p∷ser-5∷gfp translational fusion in muscle. Wild-type animals expressing a full-length ser-5 transgene with sequence coding for GFP inserted into the predicted SER-5 C terminus were examined for GFP fluorescence, as described in materials and methods.