In the endoplasmic reticulum, glycosyl transferases modify NOTCH precursors by glycosylating conserved serine and threonine residues in EGF repeats of NOTCH.
O-fucosyl transferase POFUT1 fucosylates NOTCH serine and threonine residues that conform to the consensus sequence C2-X(4-5)-S/T-C3, where C2 and C3 are the second and third cysteine residue within the EGF repeat, and X(4-5) is four to five amino acid residues of any type (Yao et al. 2011, Stahl et al. 2008, Wang et al. 2001, Shao et al. 2003).
O-glucosyl transferase POGLUT1, mammalian homolog of the Drosophila enzyme Rumi, adds a glucosyl group to conserved serine residues within the EGF repeats of NOTCH. The consensus sequence for POGLUT1-mediated glucosylation is C1-X-S-X-P-C2, where C1 and C2 are the first and second cysteine residue in the EGF repeat, respectively, while X represents any amino acid (Acar et al. 2008, Fernandez-Valdivia et al. 2011). Both fucosylation and glucosylation of NOTCH receptor precursors are essential for functionality.