TM values of RNA duplexes singly modified at positions 4, 11 or 16 of the caspase-2 guide sequence compared to native U:A base pairs in these positions. The passenger strand has either Y = C (green bars), A (blue bars) or G (red bars) opposite the modified site X, in which the R group on N2 of OG is H (X = O), propyl (X = P), or benzyl (X = B).