Polyamine Adducts with AP Sites: Interaction with DNA Polymerases and AP Endonucleases

Biological polyamines, such as spermine, spermidine, and putrescine, are abundant intracellular compounds mostly bound to nucleic acids. Due to their nucleophilic nature, polyamines easily react with apurinic/apyrimidinic (AP) sites, DNA lesions that are constantly formed in DNA by spontaneous base loss and as intermediates of base excision repair. A covalent intermediate is formed, promoting DNA strand cleavage at the AP site, and is later hydrolyzed regenerating the polyamine. Here we have investigated formation of AP site adducts with spermine and spermidine using sodium borohydride trapping technique and shown that they could persist in DNA for long enough to possibly interfere with cell's replication and transcription machinery. We demonstrate that both adducts placed internally into DNA are strongly blocking for DNA polymerases (Klenow fragment, phage RB69 polymerase, human polymerases β and κ) and direct dAMP incorporation in the rare bypass events. The internal AP site adducts with polyamines can be repaired, albeit rather slowly, by Escherichia coli endonuclease IV and yeast Apn1 but not by human AP endonuclease APE1 or E. coli exonuclease III, whereas the 3'-terminal adducts are substrates for the phosphodiesterase activities of all these AP endonucleases.