Two models of the repeating C-terminal domain of RNA polymerase II (Ac-SYSPTSPSYS-NH2; Ac-SYSPT(beta-O-GlcNAc)SPSYS-NH2) were prepared and their conformations in water studied using 1-D and 2-D H-1 NMR spectroscopies, CD spectrophotometry, fluorescence anisotropy, and molecular mechanics and dynamics calculations. The data suggest that glycosylation of the native, randomly coiled peptide with a single, biologically relevant sugar leads to the formation of a turn. This report represents the first structural study of a new class of glycoproteins monoglycosylated with N-acetylglucosamine on threonine.