Extensive photodimerization of non-adjacent pyrimidines

In a prior study we found that non-adjacent thymidyl residues in the single-stranded alternating copolymer poly[d(G-T)] are subject to photodimerization by germicidal lamp irradiation ( λ ( in max 254 nm). The maximum yield of this photoproduct was 1% of the total thymine of poly[d(G-T)]. We now report that dimer formation in this polymer is increased to 10 to 40% thymine as dimer between non-adjacent pyrimidines, using near-ultraviolet irradiation ( λ max 310 nm) with or without acetone triplet-sensitization. As previously observed for 254 nm irradiation, dimer formation was nearly absent in double-stranded poly[d(G-T) · d(C-A)]. These observations extend prior findings by demonstrating high-yield dimerization between non-adjacent pyrimidines via direct irradiation at environmentally relevant wavelengths (≥280 nm), and are potentially relevant to the mechanism of the ultraviolet light-induced targeted lt-1 frameshift mutation.