Facts About: A Heavily Glycosylated Protein in the Nucleus – RNA Polymerase II

May 01, 2024

By: Richard D. Cummings

O-GlcNAc is a major reversible modification of Ser/Thr residues found on thousands of intracellular glycoproteins in the nucleus, cytoplasm, and mitochondria, and links metabolism via GlcNAc, amino acids, and other intermediates to protein functions (1). The modification has a myriad of biological functions, but its dysregulation is implicated in neurodegenerative disorders, such as Alzheimer’s disease (2), cancer (3), lipid metabolism (4), diabetes (5), immune regulation (6), pulmonary fibrosis (7), and many others.  The modification occurs on many intracellular proteins and in some sites in competition with phosphorylation.  There are over 4,000 known glycoproteins with O-GlcNAc modifications (8-11), many of these proteins are important in regulating gene expression.  

Amazingly, the most heavily O-GlcNAcylated protein inside cells is RNA polymerase II (Pol II), found in the nucleus (12,13).  The C-terminal domain (CTD) of Pol II is greatly O-GlcNAcylated (12,14), and contains more than 200 potential glycosylation sites (15,16).  The O-GlcNAc residues are found within the consensus heptad repeat Y1S2P3T4S5P6S7 in the CTD.  This modification may help to regulate the preinitiation complex of Pol II in regulating gene expression (15).  


  1. Hart, G. W., Housley, M. P., and Slawson, C. (2007) Cycling of O-linked beta-N-acetylglucosamine on nucleocytoplasmic proteins. Nature 446, 1017-1022
  2. Huang, C. W., Rust, N. C., Wu, H. F., and Hart, G. W. (2023) Altered O-GlcNAcylation and mitochondrial dysfunction, a molecular link between brain glucose dysregulation and sporadic Alzheimer's disease. Neural Regen Res 18, 779-783
  3. Hanover, J. A., Chen, W., and Bond, M. R. (2018) O-GlcNAc in cancer: An Oncometabolism-fueled vicious cycle. J Bioenerg Biomembr 50, 155-173
  4. Lockridge, A., and Hanover, J. A. (2022) A nexus of lipid and O-Glcnac metabolism in physiology and disease. Front Endocrinol (Lausanne) 13, 943576
  5. Vaidyanathan, K., and Wells, L. (2014) Multiple tissue-specific roles for the O-GlcNAc post-translational modification in the induction of and complications arising from type II diabetes. J Biol Chem 289, 34466-34471
  6. Mannino, M. P., and Hart, G. W. (2022) The Beginner's Guide to O-GlcNAc: From Nutrient Sensitive Pathway Regulation to Its Impact on the Immune System. Front Immunol 13, 828648
  7. Vang, S., Helton, E. S., Guo, Y., Burpee, B., Rose, E., Easter, M., Bollenbecker, S., Hirsch, M. J., Matthews, E. L., Jones, L. I., Howze, P. H. t., Rajasekaran, V., Denson, R., Cochran, P., Attah, I. K., Olson, H., Clair, G., Melkani, G., Krick, S., and Barnes, J. W. (2024) O-GlcNAc transferase regulates collagen deposition and fibrosis resolution in idiopathic pulmonary fibrosis. Front Immunol 15, 1387197
  8. Hahne, H., Sobotzki, N., Nyberg, T., Helm, D., Borodkin, V. S., van Aalten, D. M., Agnew, B., and Kuster, B. (2013) Proteome wide purification and identification of O-GlcNAc-modified proteins using click chemistry and mass spectrometry. J Proteome Res 12, 927-936
  9. Ma, J., Li, Y., Hou, C., and Wu, C. (2021) O-GlcNAcAtlas: A database of experimentally identified O-GlcNAc sites and proteins. Glycobiology 31, 719-723
  10. Liu, Y., Chen, Q., Zhang, N., Zhang, K., Dou, T., Cao, Y., Liu, Y., Li, K., Hao, X., Xie, X., Li, W., Ren, Y., and Zhang, J. (2020) Proteomic profiling and genome-wide mapping of O-GlcNAc chromatin-associated proteins reveal an O-GlcNAc-regulated genotoxic stress response. Nat Commun 11, 5898
  11. Ma, J., and Hart, G. W. (2014) O-GlcNAc profiling: from proteins to proteomes. Clin Proteomics 11, 8
  12. Kelly, W. G., Dahmus, M. E., and Hart, G. W. (1993) RNA polymerase II is a glycoprotein. Modification of the COOH-terminal domain by O-GlcNAc. J Biol Chem 268, 10416-10424
  13. Lewis, B. A. (2024) The role of O-GlcNAcylation in RNA polymerase II transcription. J Biol Chem 300, 105705
  14. Comer, F. I., and Hart, G. W. (2001) Reciprocity between O-GlcNAc and O-phosphate on the carboxyl terminal domain of RNA polymerase II. Biochemistry 40, 7845-7852
  15. Parker, M. P., Peterson, K. R., and Slawson, C. (2021) O-GlcNAcylation and O-GlcNAc Cycling Regulate Gene Transcription: Emerging Roles in Cancer. Cancers (Basel) 13
  16. Lu, L., Fan, D., Hu, C. W., Worth, M., Ma, Z. X., and Jiang, J. (2016) Distributive O-GlcNAcylation on the Highly Repetitive C-Terminal Domain of RNA Polymerase II. Biochemistry 55, 1149-1158