Molecular cloning of a human UDP-galactose: GlcNAc beta 1,3GalNAc beta 1,3galactosyltransferase gene encoding an O-linked core3-elongation enzyme

Using the full-length amino-acid sequences of the human beta 1,3 galactosyl transferase (beta 3GalT)-I, -II and III enzymes as query, we have identifie d an additional member of the beta 3GalT gene family within a sequenced reg ion of the human chromosome 21 as found in GenBank. The novel human beta 3G alT-V gene included an open reading frame of 933 bp encoding a protein of 3 10 amino acids with a short N-terminal cytoplasmic tail, a single predicted transmembrane domain and a large lumenal catalytic domain. The human beta 3GalT-V protein showed 34%, 27%, 31% and 23% sequence identity with the hum an beta 3GalT-I, -II, -III and -IV enzymes, respectively. The expression of beta 3GalT-V as a recombinant protein in Sf9 insect cells confirmed the ga lactosyltransferase activity catalyzed by this enzyme. Similarly to beta 3G alT-I, -II and -III, the beta 3GalT-V enzyme used beta-linked GlcNAc as an acceptor, but unlike the former enzymes beta 3GalT-V exhibited a marked pre ference for the O-linked core3 GlcNAc beta 1,3GalNAc substrate. The beta 3G alT-V gene was mainly expressed in human small intestine and to a lesser ex tent in pancreas and testis. Although beta 3GalT-V transcripts were not det ected in normal colon tissue, based on Northern analysis, beta 3GalT-V mRNA was found in the adenocarcinoma cell line Cole 205.