The sequence specificity of UV-induced DNA damage in a systematically altered DNA sequence.

The sequence specificity of UV-induced DNA damage was investigated in a specifically designed DNA plasmid using two procedures: end-labelling and linear amplification. Absorption of UV photons by DNA leads to dimerisation of pyrimidine bases and produces two major photoproducts, cyclobutane pyrimidine dimers (CPDs) and pyrimidine(6-4)pyrimidone photoproducts (6-4PPs). A previous study had determined that two hexanucleotide sequences, 5'-GCTCAC and 5'-TATTAA, were high intensity UV-induced DNA damage sites. The UV clone plasmid was constructed by systematically altering each nucleotide of these two hexanucleotide sequences. One of the main goals of this study was to determine the influence of single nucleotide alterations on the intensity of UV-induced DNA damage. The sequence 5'-GCTCAC was designed to examine the sequence specificity of 6-4PPs and the highest intensity 6-4PP damage sites were found at 5'-GTTCCC nucleotides. The sequence 5'-TATTAA was devised to investigate the sequence specificity of CPDs and the highest intensity CPD damage sites were found at 5'-TTTTCG nucleotides. It was proposed that the tetranucleotide DNA sequence, 5'-YTCY (where Y is T or C), was the consensus sequence for the highest intensity UV-induced 6-4PP adduct sites; while it was 5'-YTTC for the highest intensity UV-induced CPD damage sites. These consensus tetranucleotides are composed entirely of consecutive pyrimidines and must have a DNA conformation that is highly productive for the absorption of UV photons.