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

Complex and hybrid N-linked carbohydrates synthesized by mammalian cel ls may possess a N-acetylglucosamine residue known as the bisecting Gl cNAc. The transfer of this residue is catalyzed by the enzyme UDP-N-ac etylglucosamine:beta-D-mannoside beta 1,4-N-acetylglucosaminyltransfer ase III (GlcNAc-TIII; EC 2.4.1.144). To begin to investigate biologica l functions for carbohydrates with a bisected GlcNAc residue, we have cloned and partially characterized the mouse gene (Mgat3) encoding Glc NAc-TIII. A rat GlcNAc-TIII-encoding cDNA was used to isolate clones f rom a mouse strain 129 Sv liver genomic DNA library. An NsiI genomic D NA fragment containing an ORF with 96% identity to rat GlcNAc-TIII was subcloned into a mammalian expression vector and transfected into Chi nese hamster ovary (CHO) cells. The transfectants expressed GlcNAc-TII I activity only when the ORF was in the sense orientation. Southern an alysis showed that Mgat3 is present in a single copy in the mouse geno me. Mapping by restriction-fragment length polymorphism analysis of ba ckcross progeny located Mgat3 to mouse chromosome 15, at a position ho mologous with region 22q12.3-q13.1 in the human genome. Northern analy ses of adult tissues showed that Mgat3 is expressed at high levels in kidney and brain, and at lower levels in many other tissues.