CLONING OF A XENOPUS-LAEVIS MUSCARINIC RECEPTOR ENCODED BY AN INTRONLESS GENE

The Xenopus laevis oocyte has endogenous sites that bind muscarinic ag onists, which have been pharmacologically characterized as M3 and/or M 1 receptor subtypes. In order to define the molecular identity of the receptor protein we have analyzed a Xenopus oocyte cDNA library and cl oned a 2.9 kb cDNA fragment encoding a muscarinic receptor (xMR). The deduced amino acid sequence reveals a protein of 484 residues with an apparent molecular weight of 54,188 Da. Amino acid comparison with pre viously cloned mammalian muscarinic receptors showed a 78% identity wi th the human m4 subtype, presenting at the same time clustered differe nces within the amino-terminal region and third intracellular loop. Ge nomic Southern analysis displayed the presence of one main gene belong ing to this subtype, and the PCR analysis revealed an intronless gene.