title: cDNAs for the postsynaptic 43-kDa protein of Torpedo electric organ encode two proteins with different carboxyl termini.
abstract: Postsynaptic membranes isolated from Torpedo electric organ are highly enriched in the nicotinic acetylcholine receptor and a nonreceptor protein of 43 kDa; the distribution of the 43-kDa protein and the receptor is coextensive in the electrical membrane. As a first step in understanding the regulation of 43-kDa protein expression, we have isolated and characterized 43-kDa protein cDNAs. A lambda gt11 cDNA library was constructed from Torpedo californica electric organ mRNA and screened with a pool of 26-mer oligonucleotides encoding a short tryptic fragment of the 43-kDa synaptic protein. Positive clones were purified and sequenced; the amino acid sequences were deduced, and they matched chemically determined protein sequences of the 43-kDa protein. Two distinct classes of cDNAs were obtained; one class encoded a 43-kDa protein of 389 amino acids with a calculated molecular mass of 43,988 daltons, and another class encoded a second 43-kDa protein containing 23 additional amino acids at the C terminus. Therefore, it appears that two 43-kDa proteins with different carboxyl termini are encoded by separate mRNAs. Consistent with this idea, blot hybridization analysis revealed multiple polyadenylylated 43-kDa mRNAs in electric organ. One polyadenylylated mRNA of approximately equal to 2.0 kilobases in length was apparent in both embryonic day-11 chick muscle and the mouse muscle cell line BC3H1.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000235:genetics*; D004557:Electric Organ / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D013570:Synaptic Membranes / Q000378:metabolism; D014101:Torpedo / Q000235:genetics*
chemical_list: D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D004247:DNA