▁detailed ▁studies ▁of ▁metal ▁ion - medi ated ▁catal ysis ▁in ▁E co R V ▁have ▁led ▁to ▁the ▁following ▁proposed ▁catal yt ic ▁mechanism . ▁It ▁has ▁been ▁suggested ▁that ▁during ▁the ▁hydro ly s is ▁of ▁DNA ▁by ▁E co R V ▁the ▁catal yt ic ▁resid ue ▁L ys - 9 2 ▁stabil izes ▁and ▁orient s ▁the ▁attack ing ▁water ▁nucle oph ile , ▁while ▁the ▁car box yl ate ▁of ▁Asp - 9 0 ▁stabil izes ▁the ▁leaving ▁hydro x ide ▁an ion ▁through ▁to ▁coord ination ▁of ▁M g 2 + . ▁ ▁Furthermore , ▁en zym atic ▁function ▁is ▁dependent ▁upon ▁the ▁correct ▁position ▁of ▁the ▁Asp - 7 4 ▁resid ue , ▁suggesting ▁has ▁a ▁role ▁in ▁increasing ▁the ▁nucle oph il icity ▁of ▁the ▁attack ing ▁water ▁mole c ule . ▁ ▁As ▁a ▁result ▁of ▁the ▁site - mut agen esis ▁experiments ▁previously ▁out lined , ▁it ▁is ▁thus ▁proposed ▁that ▁L ys - 1 2 5 , ▁Asp - 1 2 3 , ▁and ▁Asp - 1 0 8 ▁of ▁H ind III ▁function ▁similarly ▁to ▁L ys - 9 2 , ▁Asp - 9 0 , ▁and ▁Asp - 7 4 ▁in ▁E co R V , ▁respectively . ▁ ▁L ys - 1 2 5 ▁positions ▁the ▁attack ing ▁water ▁mole c ule ▁while ▁Asp - 1 0 8 ▁impro ves ▁its ▁nucle oph il icity . ▁ ▁Asp - 1 2 3 ▁coordinates ▁to ▁M g 2 + ▁which