Evidence of the Involvement of O-GlcNAc-modified Human RNA Polymerase II CTD in Transcription in Vitro and in Vivo

The RNA polymerase II C-terminal domain (CTD), which serves as a scaffold to recruit machinery involved in transcription, is modified post-translationally. Although the O -GlcNAc modification of RNA polymerase II CTD was documented in 1993, its functional significance remained obscure. We show that O -GlcNAc transferase (OGT) modified CTD serine residues 5 and 7. Drug inhibition of OGT and OGA ( N -acetylglucosaminidase) blocked transcription during preinitiation complex assembly. Polymerase II and OGT co-immunoprecipitated, and OGT is a component of the preinitiation complex. OGT shRNA experiments showed that reduction of OGT causes a reduction in transcription and RNA polymerase II occupancy at several B-cell promoters. These data suggest that the cycling of O -GlcNAc on and off of polymerase II occurs during assembly of the preinitiation complex. Our results define unexpected roles for both the CTD and O -GlcNAc in the regulation of transcription initiation in higher eukaryotes. Background: Modifications of the RNA polymerase II CTD are necessary for transcriptional regulation. Results: Perturbation of O -GlcNAc addition and removal showed transcription defects in vitro and in vivo . Conclusion: O -GlcNAc modification of the CTD functions in transcription initiation. Significance: These data provide an additional modification of the CTD that acts before the initiation of transcription.