[Highly effective complementary addressed laser modification (cleavage) of oligodeoxynucleotides]

Complementary addressed nonlinear photomodification of oligodeoxynucleotide dAGAGTATTGACTTA ("target") has been carried out by means of fluorescent derivatives of oligonucleotide dpAATACTCT ("addressed chromophore"). Three different ethidium derivatives were used as a chromophore. The photomodification was induced by nitrogen laser radiation (337 nm, 15 MW/cm2), which led to the target cleavage in the addressation region with the yield of the main fragment (8 bases long) about 10%, formation of specific covalent adduct target-addressed chromophore with the yield 20-70%, "hidden" (not revealed by gel electrophoresis) target damages with 7-27% yield (for different chromophores). The total yield of specific (i. e. localized in the vicinity of the addressation site) modification was 50-80%. The target cleavage and hidden damage generation are optically nonlinear processes. Piperidine treatment of the irradiated samples caused addressed cleavage of the target with up to 40% yield. All kinds of observed modification are not effected by high concentrations of free radical scavengers, 1,3 M t-BuOH or 10 mM cystamine. The bulk of the data is in agreement with the mechanism of nonlinear photomodification (the cleavage and hidden damage generation) based on the transfer of two-photon excitation energy from the chromophore to the target.