A SEQUENCE-SPECIFIC ALKALI-LABILE PHOTOLESION MAPPING TO ADENINE IN SINGLE-STRANDED-DNA

Following UV irradiation at 254 nm and treatment with hot piperidine, single-stranded 49-mer and 12-mer oligodeoxyribonucleotides have been shown by gel-sequencing experiments to contain a prominent alkali-labi le cleavage site that maps to adenine in the sequence element 5'-TTGAT C-3'. This behavior is abolished by single base substitutions within t he photoreactive tract and does not occur with duplex DNA. The distinc tive properties of the photolesion are consistent with the formation o f an abasic site through initial loss of a photomodified adenine base of unknown structure. The presence of an abasic site is supported by t he observations that the alkaline cleavage fragments are terminally ph osphorylated and that strand scission can also be effected by spermidi ne and the tripeptide Lys-Trp-Lys.