PCR amplification of 4'-thioDNA using 2'-deoxy-4'-thionucleoside 5'-triphosphates.

2'-Deoxy-4'-thioribonucleic acid (4'-thioDNA) having a sulfur atom instead of an oxygen atom in the furanose ring has a nuclease resistance and hybridization ability higher than that of natural DNA. Despite its great potential for various biological applications, a long 4'-thioDNA having all four kinds of 2'-deoxy-4'-thionucleosides has not been reported. In this study, we describe systematic analysis of the incorporation of 2'-deoxy-4'-thionucleoside 5'-triphosphates (dSNTPs) using various DNA polymerases. We found that family B DNA polymerases, which do not have 3'→5' exonuclease activity, could efficiently incorporate dSNTPs via single nucleotide insertion and primer extension. Moreover, 104-mer PCR product was obtained even under the conditions in the presence of all four kinds of dSNTPs when KOD Dash DNA polymerase was used. The resulting PCR product was converted into a natural dsDNA by using PCR with dNTPs, and sequencing of the natural dsDNA revealed that the PCR cycle successfully proceeded without losing the sequence information of the template. To the best of our knowledge, this is the first example of accurate PCR amplification of highly modified DNA in the presence of only unnatural dNTPs.