The nicotinic acetylcholine receptor (AChR) from fish electric organ has a subunit structure of α2βγδ, and this is thought to be also the case for the mammalian skeletal muscle AChR 1-3. By cloning and sequencing the complementary or genomic DNAs, we have previously elucidated the primary structures of all four sub-units of the Torpedo californica electroplax4-6 and calf muscle AChR 7-10 and of the α- and γ-subunits of the human muscle AChR7,11; the primary structures of the γ-subunit of the T. californien AChR12 and the α-subunit of the Torpedo marmorata AChR13,14 have also been deduced elsewhere. We have now cloned DNA complementary to the calf muscle messenger RNA encoding a novel polypeptide (the ε-subunit) whose deduced amino-acid sequence has features characteristic of the AChR subunits and which shows higher sequence homology with the γ-subunit than with the other subunits. cDNA expression studies indicate that the calf ε-subunit, as well as the calf γ-subunit, can replace the Torpedo γ-subunit to form the functional receptor in combination with the Torpedo α-, β- and δ-subunits.
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