title: Alternatively spliced RNAs encode several isoforms of CD46 (MCP), a regulator of complement activation.
abstract: Five alternative cDNA clones were isolated for CD46, also known as the membrane cofactor protein (MCP) for the factor I-mediated cleavage of the complement convertases. One of these cDNA clones (a) was identical to an earlier MCP clone. The other four CD46 clones contained the four NH2-terminal short consensus repeat (SCR) units of MCP, but differed at the region encoding the carboxyl-terminal of the protein which includes an extracellular segment rich in Ser, Thr, and Pro residues, a hydrophobic membrane-spanning domain, and a 33 amino acid cytoplasmic tail. The different CD46 cDNAs have variously: (b) inserted a 93 base pair (bp) exon resulting in a new cytoplasmic tail of 26 amino acids; (c) deleted a 42 bp exon from the extracellular Ser/Thr rich region: (d) used a cryptic splice acceptor sequence to delete 37 bp from an exon encoding transmembrane sequence; or (e) failed to splice the intron after the four SCR units. These were shown by northern blot and polymerase chain reaction to arise by alternative splicing of CD46 RNA. Forms (a), (b), and (c) of CD46 RNA are common in placental RNA, but (d) was rare, and (e) was incompletely processed and therefore aberrant. The polymerase chain reaction (PCR) was used to map the sites of the intron/exon junctions and demonstrate further possible splice variants of CD46. The alternative RNAs for CD46 may correlate to the different isoforms of CD46 found in different tissues, tumors, and in serum.
authors.affiliation: Department of Pathology, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: D F
authors.initials: DF
authors.lastname: Purcell
authors.forename: S M
authors.initials: SM
authors.lastname: Russell
authors.forename: N J
authors.initials: NJ
authors.lastname: Deacon
authors.forename: M A
authors.initials: MA
authors.lastname: Brown
authors.forename: D J
authors.initials: DJ
authors.lastname: Hooker
authors.forename: I F
authors.initials: IF
authors.lastname: McKenzie
mesh_terms: D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000235:genetics*; D000943:Antigens, Differentiation / Q000235:genetics*; D001483:Base Sequence; D015152:Blotting, Northern; D003167:Complement Activation; D004247:DNA / Q000302:isolation & purification; D005091:Exons; D007438:Introns; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins / Q000235:genetics*; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D012326:RNA Splicing; D012333:RNA, Messenger / Q000032:analysis
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D004247:DNA