Spectroscopic study of the interaction of actinomycin D with oligonucleotides carrying the central base sequences -XGCY- and -XGGCCY- using multivariate methods.

The interactions of actinomycin D (ACTD) with the oligonucleotides 5'-CAAAGCTTTG-3', 5'-CATGGCCATG-3' and 5'-TATGGCCATA-3' were investigated by means of acid-base titrations and mole-ratio and melting experiments monitored by molecular absorption and circular dichroism (CD) spectroscopies. For each experiment, CD and molecular absorption spectra were recorded at each point in the experiment, and later analyzed via appropriate multivariate data analysis methods. The study of the interactions between these oligonucleotides and ACTD at 25 degrees C showed the formation of an interaction complex with a stoichiometry of 1:1 (ACTD:duplex) and values for the log(formation constant) of 5.1+/-0.3, 6.4+/-0.2, and 5.6+/-0.2, respectively. An additional interaction complex at higher temperatures was also detected, which might be related to the single-stranded forms of the oligonucleotides.