Damage repertoire of the Escherichia coli UvrABC nuclease complex includes abasic sites, base-damage analogues, and lesions containing adjacent 5' or 3' nicks.

ABSTRACT

Using oligonucleotide synthesis, we demonstrate a rapid and efficient method for the construction of DNA duplexes containing defined DNA lesions at specific positions. These DNA lesions include apyrimidinic sites, reduced apyrimidinic sites, and base-damage analogues consisting of O-methyl- or O-benzylhydroxylamine-modified apyrimidinic sites. A 49 base pair DNA duplex containing these lesions was specifically incised by the UvrABC nuclease complex. The incision sites occurred predominantly at the eighth phosphodiester bond 5' and the fifth phosphodiester bond 3' to the lesion. Multiple incisions were observed 3' to the lesion. The extent of DNA incisions was base-damage analogues greater than reduced apyrimidinic sites greater than apyrimidinic sites. Introduction of 3' or 5' nicks at the site of a base-damage analogue by treatment of these substrates with either endonuclease III or endonuclease IV reduced, but did not abolish, subsequent incision by the UvrABC complex, whereas introduction of a 3' nick at an abasic site increased the incision efficiency of the UvrABC complex. These data demonstrate a convergence of base and nucleotide excision repair pathways in the removal of specific base damages.