Effects of vinylphosphonate internucleotide linkages on the cleavage specificity of exonuclease III and on the activity of DNA polymerase I

We have previously reported the synthesis of vinylphosphonate-linked thymidine dimers and their incorporation into synthetic oligonucleotides to create vinylphosphonate internucleotide linkages in the DNA. Such linkages have a profound effect on DNA backbone rotational flexibility, and we have shown that the PcrA helicase, which requires such flexibility, is inhibited when it encounters these linkages on the translocating strand. In this study, we have investigated the effects of these linkages on the dsDNA specific exonuclease III and on the ssDNA specific mung bean nuclease to establish whether our modification confers resistance to nucleases making it suitable for antisense therapy applications. We also investigated the effect on DNA polymerase I to establish whether we could in the future use this enzyme to incorporate these linkages in the DNA. Our results show that a single modification does not affect the activity of DNA polymerase I, but four vinylphosphonate linkages in tandem inhibit its activity. Furthermore, such linkages do not confer significant nuclease resistance to either exonuclease III or mung bean nuclease, but unexpectedly, they alter the cleavage specificity of exonuclease III.