SEQUENCE AND FUNCTIONAL EXPRESSION OF A SINGLE ALPHA-SUBUNIT OF AN INSECT NICOTINIC ACETYLCHOLINE-RECEPTOR

We report the isolation and sequence of a cDNA clone that encodes a locust (Schistocerca gregaria) nervous system nicotinic acetylcholine receptor (AChR) subunit (alpha-L1). The calculated molecular weight of the unglycosylated polypeptide, which contains in the proposed extracellular domain two adjacent cysteine residues which are characteristic of alpha (ligand binding) subunits, is 60 641 daltons. Injection into Xenopus oocytes, of RNA synthesized from the clone in vitro, results in expression of functional nicotinic receptors in the oocyte membrane. In these, nicotine opens a cation channel; the receptors are blocked by both alpha-bungarotoxin (alpha-Bgt) and kappa-bungarotoxin (kappa-Bgt). Reversible block of the expressed insect AChR by mecamylamine, d-tubocurarine, tetraethylammonium, bicuculline and strychnine has also be observed. These date are entirely consistent with previously reported electrophysiological studies on in vivo insect nicotinic receptors and also with biochemical studied on an alpha-Bgt affinity purified locust AChR. Thus, a functional receptor exhibiting the characteristic pharmacology of an in vovo insect nicotinic AChR can be expressed in Xenopus oocytes by injections with a single subunit RNA.