Post-translational modification by O-GlcNAc: another way to change protein function

Modification of intracellular proteins by the beta-linkage of the monosaccharide, N-acetylglucosamine to serine or threonine hydroxyls (O-GlcNAc) is abundant and reversible. Although many proteins bear this post-translational covalent modification, the changes in function of the proteins as a result of this modification are only starting to be understood. In this article, we describe how aspects of the flux from the glucose backbone to this modification are modified and how the cellular activity and content of the GC-box binding transcription factor, Sp1, is altered by O-glycosylation. The association of the enzyme that puts on the O-GlcNAc modification with the bi-functional enzyme that removes this modification is discussed relative to the transition between transcriptional repression and activation.