The abasic site is the most common lesion in DNA and is thought to play a critical role in mutagenesis. However, a general chemical method for the site-specific generation of true abasic sites in oligodeoxynucleotides has been lacking. We now describe a procedure which permits the postsynthetic generation of abasic sites in single- or double-stranded DNA oligomers without regard to their base composition. An appropriately protected 3-deoxyhexitol was synthesized and used as the monomer that was incorporated into DNA oligomers using the standard phosphoramidite method for automated DNA synthesis. The resulting stable diol-containing oligonucleotides were purified by HPLC and converted quantitatively into the corresponding abasic DNA sequences by mild periodate oxidation. The abasic site in DNA was found to be relatively stable at room temperature, but was completely cleaved when treated with putrescine at 95 degrees C. Identification of the major degradation products was accomplished by gel electrophoresis, HPLC isolation, and characterization by electrospray ionization mass spectrometry. The thermal stabilities of duplex oligonucleotides containing a natural abasic site were studied, and the results were compared with those from oligomers containing T/dA, F/dA, or the precursor diol opposite dA at the same site.

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