"The modification of nuclear and cytoplasmic proteins by covalent attachment of N-acetylglucosamine (O-GlcNAc) to serine or threonine residues is emerging as a crucial regulatory posttranslational modification similar to phosphorylation. O-GlcNAc is essential for cell survival and is implicated in key biological processes (e. g., nutrient sensing, protein regulation and gene expression) and human diseases (e. g., diabetes, Alzheimer’s disease and cancer). In contrast to conventional protein glycosylation, O-GlcNAcylation is not further elaborated into complex glycans and occurs on intracellular proteins.Despite its biological importance, the functional roles and molecular details of O-GlcNAc modification remain to be elucidated; furthermore, no consensus sequence has been established for the site of glycosylation.With the goal of answering these questions, we propose herein novel chemical and enzymatic strategies to recapitulate and probe O-GlcNAcylation in vitro and in vivo. On the basis of the ""tag-and-modify"" approach to site-selective protein modification developed in Professor Davis' group, these investigations will be directed to enable the identification of O-GlcNAc-modified proteins and their specific glycosylation sites. Such strategies can be used as a powerful tool for elucidating the, as yet largely unknown, functional significance and molecular mechanisms of this dynamic posttranslational modification.On a professional basis, this multidisciplinary project will surely contribute significantly to the career development of the researcher, by adding different training and research competences along with complementary skills at an advanced level."