Updated project metadata. Complex molecular mechanisms ensure cellular homeostasis between nutrient sensing and energy metabolism. Strong evidence from many laboratories supports a role for the hexosamine biosynthetic pathway (HBP) and its end product, UDP-GlcNAc, as important nutrient sensors. Isotopic photocleavable tagging for O-GlcNAc profiling (isoPTOP) was performed for quantitative and site specific identification of O-GlcNAcylation upon glucose mediated nutrient fluctuation. Mammalian target of Rapamycin complex 1（mTORC1）is a metabolic hub, which can sense the availability of various nutrients. We found that Raptor, the scaffold of the mTORC1 complex, is O-GlcNAcylated at T700. Our finding provides a novel mechanism that UDP-GlcNAc mediates glucose signal to mTORC1 by O-GlcNAcylating Raptor at T700 to regulate mTORC1 activity and cell growth.