To investigate which positions in a DNA oligonucleotide would exert the largest effect when substituted by an LNA analog, we designed LNA/DNA mix-mer mutants based on LNA2, which is the most efficient LNA/DNA mix-mer in our experiments and would give a good read-out. When the two LNA substitutions were moved two positions more inward (L2-1), compared to LNA2, frameshift efficiency decreased to 6.7% ( Figure 6 ). However, when the LNA modifications were moved another two positions more inward (L2-2), activity dropped to 2.7% ( Figure 6 ) which is comparable to an unmodified DNA oligonucleotide. Similarly, when the LNA groups were introduced at the other end of the oligonucleotide, activity was as low as DNA18 ( Figure 6 ). Finally, L2-4, in which the first and fourth position were LNA, was only half as efficient as LNA2. These results indicate that the choice of the location of the LNA modifications is crucial for the frameshift-inducing efficiency of an oligonucleotide.