* A series of reactions occur on the core M3 O-mannosyl trisaccharide of α-dystroglycan (DAG1), and these elongate the core structure.
* Among these, first, two phospho-ribitols are added to the trisaccharide core. The first phospho-ribitol is added to GalNAc by FKTN/fukutin. The second ribitol is added by Fukutin-related protein/FKRP. Together, this results in the ribose 5-phosphate tandem repeat of DAG1.
* This unit is then primed by TMEM5 () and B3GAT1 (formerly B4GAT1).
* The core M3 structure can then be further extended by repeating GlcAβ(1-3)Xylα(1-3) units. This polymerization bifunctional GTs, LARGE1 (formerly LARGE) and/or its paralog LARGE2 (formerly GYLTL1B) in the Golgi apparatus.