Abstract
Although the O-linked N-acetylglucosamine (O-GlcNAc) modification of the RNA polymerase II C-terminal domain was described 20 years ago, the function of this RNA polymerase II (pol II) species is not known. We show here that an O-GlcNAcylated pol II species (pol IIγ) exists on promoters in vitro Inhibition of O-GlcNAc-transferase activity and O-GlcNAcylation prevents pol II entry into the promoter, and O-GlcNAc removal from pol II is an ATP-dependent step during initiation. These data indicate that O-GlcNAc-transferase activity is essential for RNA pol II promoter recruitment and that pol II goes through a cycling of O-GlcNAcylation at the promoter. Mass spectrometry shows that serine residues 2 and 5 of the pol II C-terminal domain are O-GlcNAcylated, suggesting an overlap with the transcription factor IIH (TFIIH)-dependent serine 5 phosphorylation events during initiation and P-TEFb (positive transcriptional elongation factor b) events during elongation. These data provide unexpected and important insights into the role of a previously ill-defined species of RNA polymerase II in regulating transcription.