Furocoumarin-oligonucleotide interaction: Kinetics, selectivity, and mechanism of the furocoumarin photoaddition reaction to oligonucleotide intercalation sites

The interaction and subsequent photoaddition reaction on UVA irradiation of 4.4'-dimethyl-5-methoxyangelicin and 4.4'-dimethyl-5-methoxypsoralen to tw elve synthetic oligonucleotides was studied. A new approach was developed w hich allows: (a) accurate determination of the kinetics constant of the ove rall photoaddition process to each oligonucleotide; (b) identification of t he different types of intercalation sites, individualized by a combination of two consecutive base pairs and the frequency of their appearance along t he: oligomer sequences; and (c) the value of the kinetics constant relative to each type of site to be determined. This approach also makes it possibl e to highlight the influence of sequences flanking each site that participa te in the photoaddition process. Thus, the possibility of discriminating wh ich sites are active in the photoaddition reaction and their contribution t o the overall process appears to be a useful tool Tot studying the correlat ion between furocoumarin photocombination with DNA and the consequent biolo gical effects.