Allelic variants of acetylcholinesterase: Genetic evidence that all acetylcholinesterase forms in avian nerves and muscles are encoded by a single gene

Two acetylcholinesterase (AcChoEase) polypeptide chains, α and β, are expressed in avian nerves and muscles with apparent molecular masses of 110 and 100 kDa, respectively. We now show that individual quails express α, β, or both AcChoEase polypeptide chains. By mating studies we show that the two AcChoEase polypeptides are autosomal and segregate as codominant alleles in classical Mendelian fashion. Biochemical studies of the two allelic AcChoEase polypeptides indicate that they have the same turnover number, have the same K(m) for acetylcholine, are immunoprecipitated to the same extent with a monoclonal anti-AcChoEase antibody, and can assemble with equal efficiency into multimeric forms. Thus there are no obvious functional differences between the two alleles. In heterozygotes, the rates of synthesis of the two polypeptides are identical, suggesting that there are no differences in expression of these two genes. Within an individual, nerves and muscles always express the same AcChoEase alleles. Analysis of the allelic composition of the multiple AcChoEase forms isolated from muscle indicates that all AcChoEase forms are comprised of the same allelic chains. In contrast to the nicotinic acetylcholine receptors that appear to be encoded by complex multigene families, our studies on AcChoEase show that all forms of this important synaptic component in electrically excitable cells are encoded by a single gene. Thus differences in assembly and localization of the multiple synaptic forms of AcChoEase must arise through posttranscriptional events, posttranslational modifications of a similar AcChoEase polypeptide chain or both.