Chemical synthesis of oligonucleotides containing the (6-4) photoproduct at the thymine-cytosine site and its repair by (6-4) photolyase.

A phosphoramidite building block of the T(6-4)C photoproduct was synthesized. One of the differences from T(6-4)T was formation of cytosine hydrates by UV irradiation, and the other was acylation of the amino function with the capping reagent. The capping step was omitted to improve the yield of the desired oligonucleotides. Characterization of the (6-4) photolyase using one of the oligonucleotides revealed that this enzyme restores the pyrimidines in T(6-4)C to their original structures.