<p>Imino proton assignments of C11/20/23T using 1D <sup>15</sup>N-filtered experiments on site-specific <sup>15</sup>N-labeled oligonucleotides. Each site-specifically labeled cytosine is shown above its corresponding spectrum. The assignment of all cytosine imino protons is shown above the 1D <sup>1</sup>H spectrum of C11/20/23T. All samples are at pH 5.5. NMR experiments were performed at 7°C.</p