[Sequence specificity modification of double-stranded DNA with an alkylating derivative of oligodeoxyribonucleotide pT(CT)6].

It is shown that in slightly acidic solution (pH approximately 5.3) reagent CIRCH2NHpT(CT)6 (RCl = -C6H4-N(CH3)CH2CH2Cl) modifies a double-stranded DNA fragment (120 b. p.) containing A(GA)6.T(CT)6 sequence at a single nucleotide residue, viz. G29 located near to this sequence in the DNA chain. The location of this modification point suggests formation of a triple-stranded reactive complex with parallel orientation of the pyrimidine oligonucleotide moiety of the reagent and pyrine sequence of the target DNA. Analysing the modification extent dependence of the reagent concentration the association constant Kx between the reagent and DNA was calculated (Kx = (0.95 +/- 0.03).10(5) M-1, 25 degrees C, pH = 5.3, [NaCl] = 0.1 M). The modification by the reagent ClRCH2NHpT(m5CT)6 has the same quantitative characteristics as in the case of ClRCH2NHpT(CT)6.