Abstract
The effect of ATP on the first step of excision repair of ultraviolet damage in DNA has been studied using toluene-treated E. coli. During postirradiation incubation, five to six times more single-strand breaks are formed in DNA in the presence of exogenous ATP than in its absence. The ATP-dependent as well as the ATP-independent endonucleolytic activities appear to be catalyzed by the same enzyme since both activities are almost completely absent in uvrA and uvrB mutants. An ATP-dependent endonucleolytic activity has been detected in nonirradiated toluene-treated E. coli. It is concluded that ATP is required in vivo for either the incision step of repair or an enzymatic reaction preceding it.