Stereochemistry of cleaved DNA. Cleavage of DNA by EcoRV endonuclease results in overall inversion of the stereochemical configuration at the phosphorus atom, as indicated by the stereochemistry of the phosphorus atom bound to one bridging oxygen atom, one16O, one18O, and one sulfur atom. Two possible products are shown, only one of which is observed, indicating direct attack of water at the phosphorous atom.