Alkylation of nucleic acid components with ethylenimine and its derivatives. IV. Alkylation of homopolynucleotides and DNA

: Alkylation of homopolynucleotides and DNA by thio TEPA and monoaziridine diethyl phosphate was studied. The modification affected nucleic bases and terminal phosphate groups but not internucleotide phosphate groups. It was shown that the main center of modification in poly(A) was the N1 atom, whereas the products of N6- and N3-alkylations were formed in smaller amounts. In poly(G), the alkylation proceeded predominantly at the N7 and, insignificantly, at the N1 atom of guanine; the pyrimidine N3 atom is alkylated poorly in poly(C) and even worse in poly(U). In the case of DNA, the major alkylated sites are the guanine N7 and the adenine N3; this results in DNA denaturation and the subsequent formation of products modified at N1 and N6 of adenine, N1 of guanine, and N3 of cytosine. An increase in the pH and ionic strength of the solution as well as the DNA denaturation decrease the reaction rate, whereas ultrasonic fragmentation enhances it. Upon alkylation, melting temperatures decrease, CD and UV spectra change, and DNA luminescence appears. To separate the reaction mixtures and identify the DNA alkylation products, chemical hydrolysis, ion-exchange and reverse-phase HPLC, and UV spectroscopy were used.