Acetylcholine receptor subunits transit a precursor pool before acquiring alpha-bungarotoxin binding activity.

We have developed methods for the rapid immunoprecipitation of acetylcholine receptor from the clonal mouse cell line BC3H-1. One antiserum, anti-alpha-bungarotoxin, precipitates receptors to which alpha-bungarotoxin is bound. A second antiserum prepared against sodium dodecyl sulfate-denatured receptor precipitates receptor polypeptides independent of toxin binding activity. We have used these sera to analyze the products of synthesis in vivo after short pulses of [35S]methionine. Acetylcholine receptor polypeptides of synthesized during a 5-min pulse require 15 min before they become fully active for alpha-bungarotoxin binding. These experiments identify an early step in the assembly of functional acetylcholine receptor and suggest a novel mechanism by which receptor synthesis may be controlled post-translationally.