Hybridization kinetics of oligodeoxyribonucleotides with a d(GCGAAGC) hairpin at the 3'-end

In order to protect them against enzymatic attack of serum in the antisense strategy, oligodeoxyribonucleotides can be protected on their 3'-side by the sequence d(GCGAAGC) which spontaneously forms a hairpin which is known for its extraordinary stability with regard to thermal denaturation or nuclease degradation (I. Hirao, G. Kawai, S. Yoshizawa, Y. Nishimura, Y. Ishido, K. Watanabe and K. Miura, Nucleic Acids Res. 22, 576-582 (1994)). By contrast, the hairpin does not prevent hybridization of the 5'-stem part of the oligonucleotide to a target DNA strand. As soon as this pairing occurs, the stability of the hairpin is disrupted. Its opening rate, followed by its pairing if possible, is of the same order than that of hybridization of the stem part.