title: Identification of a novel type of alternatively spliced exon from the acetylcholinesterase gene of Bungarus fasciatus. Molecular forms of acetylcholinesterase in the snake liver and muscle.
abstract: The venom of the snake Bungarus fasciatus contains a hydrophilic, monomeric species of acetylcholinesterase (AChE), characterized by a C-terminal region that does not resemble the alternative T- or H-peptides. Here, we show that the snake contains a single gene for AChE, possessing a novel alternative exon (S) that encodes the C-terminal region of the venom enzyme, located downstream of the T exon. Alternative splicing generates S mRNA in the venom gland and S and T mRNAs in muscle and liver. We found no evidence for the presence of an H exon between the last common "catalytic" exon and the T exon, where H exons are located in Torpedo and in mammals. Moreover, COS cells that were transfected with AChE expression vectors containing the T exon with or without the preceding genomic region produced exclusively AChET subunits. In the snake tissues, we could not detect any glycophosphatidylinositol-anchored AChE form that would have derived from H subunits. In the liver, the cholinesterase activity comprises both AChE and butyrylcholinesterase components; butyrylcholinesterase corresponds essentially to nonamphiphilic tetramers and AChE to nonamphiphilic monomers (G1na). In muscle, AChE is largely predominant: it consists of globular forms (G1a and G4a) and trace amounts of asymmetric forms (A8 and A12), which derive from AChET subunits. Thus, the Bungarus AChE gene possesses alternatively spliced T and S exons but no H exon; the absence of an H exon may be a common feature of AChE genes in reptiles and birds.
authors.affiliation: Unité des Venins, Institut Pasteur, 28 rue du Dr Roux, 75015 Paris, France.
authors.forename: X
authors.initials: X
authors.lastname: Cousin
authors.forename: S
authors.initials: S
authors.lastname: Bon
authors.forename: J
authors.initials: J
authors.lastname: Massoulié
authors.forename: C
authors.initials: C
authors.lastname: Bon
mesh_terms: D000110:Acetylcholinesterase / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017838:Bungarus / Q000235:genetics*; D002091:Butyrylcholinesterase / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D019556:COS Cells; D017173:Caenorhabditis elegans / Q000201:enzymology; D002645:Chickens; D003094:Collagen / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D005091:Exons; D006801:Humans; D007527:Isoenzymes / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D008099:Liver / Q000201:enzymology*; D051379:Mice; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000201:enzymology*; D016133:Polymerase Chain Reaction; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014162:Transfection
chemical_list: D007527:Isoenzymes; D011994:Recombinant Proteins; D003094:Collagen; D000110:Acetylcholinesterase; D002091:Butyrylcholinesterase