UBIQUITOUS AND TEMPORAL GLYCOSYLATION OF NUCLEAR AND CYTOPLASMIC PROTEINS

We have described a novel form of nuclear and cytoplasmic protein glycosylation (O-GlcNAc), which is as abundant and as transient an intracellular proteins as protein phosphorylation. O-GlcNAc consists of single, non-modified N-acetylglucosamine residues O-glycosidically attached to Ser(Thr) hydroxyl moieties at sites similar to those used by growth-factor kinases, O-GlcNAc occurs on 'hundreds' of intracellular proteins in all eukaryotes. Proteins bearing O-GlcNAc include cytoskeletal-, viral-, nuclear pore-, heal shock-, and transcriptional regulatory proteins. Available data suggest that O-GlcNAc is a regulatory modification that mediates subunit-subunit interactions and in many cases blocks phosphorylation.