UBIQUITOUS AND TEMPORAL GLYCOSYLATION OF NUCLEAR AND CYTOPLASMIC PROTEINS

We have described a novel form of nuclear and cytoplasmic protein glyc osylation (O-GlcNAc), which is as abundant and as transient an intrace llular proteins as protein phosphorylation. O-GlcNAc consists of singl e, non-modified N-acetylglucosamine residues O-glycosidically attached to Ser(Thr) hydroxyl moieties at sites similar to those used by growt h-factor kinases, O-GlcNAc occurs on 'hundreds' of intracellular prote ins in all eukaryotes. Proteins bearing O-GlcNAc include cytoskeletal- , viral-, nuclear pore-, heal shock-, and transcriptional regulatory p roteins. Available data suggest that O-GlcNAc is a regulatory modifica tion that mediates subunit-subunit interactions and in many cases bloc ks phosphorylation.