CLONING AND CHROMOSOMAL MAPPING OF THE MOUSE MGAT3 GENE ENCODING N-ACETYLGLUCOSAMINYLTRANSFERASE-III

Complex and hybrid N-linked carbohydrates synthesized by mammalian cells may possess a N-acetylglucosamine residue known as the bisecting GlcNAc. The transfer of this residue is catalyzed by the enzyme UDP-N-acetylglucosamine:beta-D-mannoside beta 1,4-N-acetylglucosaminyltransferase III (GlcNAc-TIII; EC 2.4.1.144). To begin to investigate biological functions for carbohydrates with a bisected GlcNAc residue, we have cloned and partially characterized the mouse gene (Mgat3) encoding GlcNAc-TIII. A rat GlcNAc-TIII-encoding cDNA was used to isolate clones from a mouse strain 129 Sv liver genomic DNA library. An NsiI genomic DNA fragment containing an ORF with 96% identity to rat GlcNAc-TIII was subcloned into a mammalian expression vector and transfected into Chinese hamster ovary (CHO) cells. The transfectants expressed GlcNAc-TIII activity only when the ORF was in the sense orientation. Southern analysis showed that Mgat3 is present in a single copy in the mouse genome. Mapping by restriction-fragment length polymorphism analysis of backcross progeny located Mgat3 to mouse chromosome 15, at a position homologous with region 22q12.3-q13.1 in the human genome. Northern analyses of adult tissues showed that Mgat3 is expressed at high levels in kidney and brain, and at lower levels in many other tissues.