title: Isolation of a cDNA encoding a murine UDPgalactose:beta-D-galactosyl- 1,4-N-acetyl-D-glucosaminide alpha-1,3-galactosyltransferase: expression cloning by gene transfer.
abstract: We have developed a genetic approach to isolate cloned cDNA sequences that determine expression of cell surface oligosaccharide structures and their cognate glycosyltransferases. A cDNA library was constructed in a mammalian expression vector by using mRNA from a murine cell line known to express a UDPgalactose:beta-D-galactosyl-1,4-N-acetyl-D-glucosaminide alpha-1,3-galactosyltransferase [(alpha 1-3)GT; EC 2.4.1.151]. This library was transfected into COS-1 cells, which lack expression of (alpha 1-3)GT. Transfected cells containing functional (alpha 1-3)GT cDNAs were detected and isolated with a lectin that recognizes the surface-expressed glycoconjugate product of the (alpha 1-3)GT enzyme. One cloned (alpha 1-3)GT cDNA was rescued from lectin-positive transfected cells. This cDNA contains a single long open reading frame that predicts a 394-amino-acid protein. No significant primary structure similarities were identified between this protein and other known sequences. However, the protein predicts a type II transmembrane topology similar to two other mammalian glycosyltransferases. This topology places the large COOH-terminal domain within the Golgi lumen; this domain was shown to be catalytically active when expressed in COS-1 cells as a portion of a secreted protein A fusion peptide. Biochemical analysis confirmed that this enzyme catalyzes a transglycosylation reaction between UDP-Gal and Gal(beta 1-4)GlcNAc to form Gal(alpha 1-3)Gal(beta 1-4)GlcNAc. This cloning approach may be generally applicable to the isolation of cDNAs encoding other mammalian glycosyltransferases.
authors.affiliation: Howard Hughes Medical Institute, University of Michigan Medical Center, Ann Arbor, MI 48109-0650.
authors.forename: R D
authors.initials: RD
authors.lastname: Larsen
authors.forename: V P
authors.initials: VP
authors.lastname: Rajan
authors.forename: M M
authors.initials: MM
authors.lastname: Ruff
authors.forename: J
authors.initials: J
authors.lastname: Kukowska-Latallo
authors.forename: R D
authors.initials: RD
authors.lastname: Cummings
authors.forename: J B
authors.initials: JB
authors.lastname: Lowe
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002846:Chromatography, Affinity; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D005700:Galactosyltransferases / Q000235:genetics* / Q000302:isolation & purification; D015870:Gene Expression; D015723:Gene Library; D005796:Genes; D005822:Genetic Vectors; D051379:Mice; D008969:Molecular Sequence Data; D010957:Plasmids; D014162:Transfection
chemical_list: D004247:DNA; D005700:Galactosyltransferases; C047006:N-acetyllactosaminide alpha-1,3-galactosyltransferase