THE HUMAN MUSCLE NICOTINIC ACETYLCHOLINE-RECEPTOR ALPHA-SUBUNIT EXISTS AS 2 ISOFORMS - A NOVEL EXON

Analysis of acetylcholine receptor clones isolated from a humn leg muscle cDNA library, revealed that the α-subunit existed as two isoforms. A novel exon, coding for 25 amino acids, was located in the human genomic DNA sequence; its insertion into the α-subunit gives the new isoform of 462 amino acids. In additio, mRNAs for the two isoforms were found in equal proportions in poly(A)+ RNA obtained from three further sources including partially denervated and innervated human muscle and the rhabdomyosarcoma cell line TE671. Both protein isoforms can be expressed in E.coli. No evidence of a sequence related to that of the new exon was found in cDNA derived from poly(A)+ RNA isolated from fetal calf or embryonic chick muscle or Torpedo marmorata electric organ.