FACTORS INFLUENCING THE EXTENT AND SELECTIVITY OF ALKYLATION WITHIN TRIPLEXES BY REACTIVE G A MOTIF OLIGONUCLEOTIDES/

G/A motif tripler-forming oligonucleotides (TFOs) complementary to a 2 1 base pair homopurine/homopyrimidine run were conjugated at one or bo th ends to chlorambucil. These TFOs were incubated with several synthe tic duplexes containing the targeted homopurine run flanked by differe nt sequences, The extent of mono and interstrand cross-linking was com pared with the level of binding at equilibrium, Covalent modification took place within a triple-stranded complex and usually occurred at gu anine residues in the flanking double-stranded DNA, The efficiency of alkylation was dependent upon the sequence of the flanking duplex, the solution conditions, and the rate of tripler formation relative to th e rate of chlorambucil reaction, Self-association of the TFOs as paral lel duplexes was demonstrated and this did not interfere with triple s trand formation, With an optimal target, cross-linking of the tripler was very efficient when incubation was carried in a physiological buff er supplemented with the tripler selective intercalator coralyne.