A complementary DNA encoding a G protein-coupled glutamate receptor from rat brain, GluGR, was cloned by functional expression in Xenopus oocytes. The complementary DNA encodes a protein of 1199 amino acids containing a seven-transmembrane motif, flanked by large amino- and carboxyl-terminal domains. This receptor lacks any amino acid sequence similarity with other G protein-coupled receptors, suggesting that it may be a member of a new subfamily. The presence of two introns flanking the central core suggests that GluGR may have evolved by exon shuffling. Expressed in oocytes, GluGR is activated by quisqualate greater than glutamate greater than ibotenate greater than trans-1-aminocyclopentyl-1,3-dicarboxylate, and it is inhibited by 2-amino-3-phosphonopropionate. Activation is blocked by Bordella pertussis toxin. These properties are typical of some metabotropic glutamate receptors.