Mutant a subunits of Torpedo acetylcholine receptors (AChR) were constructed and expressed in Xenopus oocytes together with other normal subunits to investigate regions in the subunit that are required for subunit assembly. I have found that chimeric-alpha-subunits, consisting of the N-terminal extracellular domain of the AChR alpha-subunit, followed either by the hydrophobic transmembrane segments of GABA(A) receptor or glutamate receptor subunits, were still recognized as the AChR subunit and associated with co-expressed other normal AChR subunits, suggesting that this part of the N-terminal extracellular domain contains 'assembly signals'.