To demonstrate that the enhanced effect of LNA oligonucleotides is a general feature we designed another construct (SF462) in which the target sequence was replaced by an unrelated sequence ( Figure 4 ). LNA/DNA mix-mers were designed in which nucleotides starting from the 3 0 -end were gradually replaced by LNA ( Figure 4 ). Increasing the number of LNAs from one to two and four in these DNA oligonucleotides improved their frameshift inducing ability, reaching an apparent optimum of 7.0% with four LNA substitutions. Further increase of the LNA content to 6 nt (LD6) did not improve frameshift efficiency, but, on the other hand, LD6 also did not lead to the dramatic decrease as observed above for the LNA6 oligonucleotide applied in the SF468 construct. We suspected that (partial) self-complementarity may be limiting the effective concentration of free LNA/DNA oligonucleotides. To check this possibility, we ran all the oligonucleotides on a non-denaturing polyacrylamide gel. Figure 5 showes that the LNA6 oligonucleotide indeed migrated more slowly indicative of partial dimer formation, presumably by intermolecular base pairing of the palindromic GCGCGC sequences in each oligonucleotide (compare the migration to that of the full dimer formed by annealing of oligonucleotides DNA18 and 18DNA). The LD series, as predicted, migrated as monomers. We noted that LD2, though loaded in equal amount, based on its UV absorbance, showed a higher affinity to ethidium bromide than its counterparts. At present we have no explanation for this unexpected behavior of LD2, since its migration and therefore its conformation was identical to the other LNA/DNA mix-mers.