Synthesis and characterization of a substrate for T4 endonuclease V containing a phosphorodithioate linkage at the thymine dimer site.

A dodecadeoxyribonucleotide containing a cis-syn thymine dimer with a phosphorodithioate linkage was synthesized on a solid support using a dinucleotide coupling unit prepared by UV-irradiation of dithymidine monophosphorodithioate followed by S- and 5'-O-protection and 3'-phosphitylation. A photodimer-containing dodecamer without phosphate modification was also synthesized. The dodecamers were hybridized to the complementary sequence, and the duplexes used as substrates for T4 endonuclease V. This enzyme cleaved the phosphate-modified substrate more slowly than the unmodified duplex with the same dissociation constant.