Oligo swapping method for in vitro DNA repair substrate containing a single DNA lesion at a specific site.

Background: A wide variety of DNA lesions interfere with replication and transcription, leading to mutations and cell death. DNA repair mechanisms act upon these DNA lesions present in the genomic DNA. To investigate a DNA repair mechanism elaborately, an in vitro DNA repair substrate containing DNA lesions at a specific site is required. Previously, to prepare the substrate, phagemid ssDNA and DNA lesion-harboring oligonucleotides were employed with considerable amounts of DNA polymerase and DNA ligase. However, preparing in vitro DNA repair substrate in general is difficult and labor intensive.

Results: Here, we modified the construction method of in vitro mismatch repair substrate using a nicking-endonuclease, which produces gap corresponding to the ssDNA in the plasmid DNA, and swaps DNA lesion-containing oligonucleotide upon addition of restriction enzyme and T5 exonuclease. This modified method is able to produce in vitro DNA repair substrates containing adenine:cytosine mismatch basepair, 8-oxoG, and uracil. The DNA repair enzyme, each Fpg, hOGG1 could cleave an 8-oxoG-containing DNA substrate, the mixture of UDG and APE1 could cleave a uracil-containing DNA substrate. Omitting a column purification step, DNA repair substrates were prepared by one-pot synthesis.

Conclusions: We were able to prepare in vitro DNA repair substrates using this simple method involving restriction enzymes and T5 exonuclease. It is anticipated that this method, termed as "Oligo Swapping Method", will be valuable for understanding the DNA repair machinery.