Effect of DNA polymerase I and DNA helicase II on the turnover rate of UvrABC excision nuclease.

UvrABC excision nuclease (UvrA, UvrB, and UvrC proteins) of Escherichia coli removes nucleotide mono- and diadducts from DNA in the form of oligonucleotides 12 or 13 bases long. We find that the purified enzyme dissociates from DNA very slowly, if at all, in the absence of other proteins implicated in excision repair. Addition of DNA polymerase I and helicase II (UvrD protein) to the reaction mixture stimulates the turnover rate of the excision nuclease to a level comparable to that observed in vivo.