Co-immunoprecipitation of cMyc-SMG9 with Flag-OGT (WT) or (a) Flag-OGT-I734R (I734R), (b) Flag-OGT-I787E (I787E), (c) Flag-OGT-I787E-N791A (2M), from TRex-293 cells, followed by western blot. (d) Co-immunoprecipitation of endogenous OGA with Flag-OGT (W) or Flag-OGT-N791A (M) from TRex-293 cells, followed by western blot. (e) O-GlcNAcylation detection on CaMKMT from cells co-expressed with Flag-OGT (W) or Flag-OGT-N791A (M). HA-tagged CaMKMT was immunoprecipitated from TRex-293 cell lysate by anti-HA agarose and the O-GlcNAcylation was detected with the same GalT assay as SMG9. (f) O-GlcNAcylation detection on Flag-OGT (W), Flag-OGT-N791A (M), and Flag-HA-OGA-D175N. Flag-tagged OGT and OGA were immunoprecipitated from TRex-293 cell lysate by Flag-agarose, followed by western blot. All whole cell lysates have endogenous OGT knocked down. Blots are representative of at least three biological replicates.