[A new type of DNA modification. Specific introduction of 3'-5'-pyrophosphate internucleotide bonds]

Novel compounds--modified DNA-duplexes containing 3'-5'-pyrophosphate internucleotide bonds--have been synthesized. The synthesis was carried out by means of chemical template-guided polycondensation of 3'-5'-diphosphate of decanucleotide pTGGCCAAGCTp, which forms DNA-like duplexes as a result of self-association. 1-Ethyl-3-(3'-dimethylaminopropyl)carbodiimide was used as a condensing agent. Almost quantitative yield of polymer products was achieved by incubation of the reaction mixture for 72 hours. The pyrophosphate type of the internucleotide bonds was confirmed by complete cleavage of these polymers by trifluoroacetic anhydride. The interaction of DNA-duplexes, containing the 3'-5'-pyrophosphate bonds, with restriction endonucleases BspI, HindIII and AluI was studied. BspI and HindIII were able to hydrolyze modified duplexes giving corresponding decanucleotides, whereas AluI failed to split the duplexes.