PRIMARY STRUCTURE AND CELL-TYPE-SPECIFIC EXPRESSION OF A GUSTATORY G-PROTEIN-COUPLED RECEPTOR-RELATED TO OLFACTORY RECEPTORS

We have reported on the partial structures of a multigene family encod ing GTP-binding protein (G protein)-coupled, seven-transmembrane recep tors expressed in the tongue (Abe, K., Kusakabe, Y., Tanemura, K., Emo ri, Y., and Arai, S. (1993) FEBS Lett. 316, 253-256). Here we describe a full-length cDNA clone encoding a tongue cell-type specific recepto r. The encoded protein consists of 312 amino acid residues. In overall structure, the protein is similar to known G protein-coupled, seven-t ransmembrane receptors such as an olfactory receptor (56% identity) bu t is significantly different in part, particularly in NH2-terminal ext racellular and COOH-terminal cytoplasmic domain structures. Northern a nalysis showed that the mRNA for this protein is expressed only in the epithelium of the tongue, not in other organs. In situ hybridization experiments clearly indicated that the mRNA is expressed exclusively o n the tongue apical surface, not on the reverse side of the tongue nor in its muscle layer. Expression was also detected in the taste buds a nd surrounding cellular tissues of the fungiform and circumvallate pap illae. It is suggested that this gustatory receptor structurally relat ed to olfactory receptors may be a candidate for a taste receptor.