▁I ▁removes ▁the ▁T ▁and ▁some ▁nucle ot ides ▁on ▁the ▁ 3 ' ▁str and ▁and ▁then ▁res yn thes ises ▁the ▁patch . ▁ ▁Additionally , ▁GT ▁mismatch es ▁can ▁lead ▁to ▁C - to - T ▁transition ▁mut ations ▁if ▁not ▁rep a ired . ▁VS R ▁rep airs ▁the ▁mismatch es ▁in ▁favour ▁of ▁the ▁G - cont aining ▁str and . ▁In ▁E scher ich ia ▁col i , ▁this ▁end on uc lease ▁n icks ▁double - str and ed ▁DNA ▁within ▁the ▁sequence ▁CT ( AT ) GN ▁or ▁N T ( AT ) GG ▁next ▁to ▁the ▁th ym id ine ▁resid ue , ▁which ▁is ▁mismatch ed ▁to ▁ 2 '- de ox y gu anos ine . ▁The ▁inc ision ▁is ▁mismatch - dependent ▁and ▁str and ▁specific . ▁ ▁Str ucture ▁The ▁structure ▁of ▁VS R ▁is ▁similar ▁to ▁the ▁core ▁structure ▁of ▁restriction ▁end on uc leases , ▁which ▁have ▁a ▁ 3 - layer ▁alpha / beta / alpha ▁topology . ▁ ▁VS R ▁has ▁three ▁a rom atic ▁resid ues ▁( P he 6 7 , ▁Tr p 6 8 ▁and ▁Tr p 8 6 ), ▁which ▁inter cal ate ▁into ▁the ▁major ▁gro ove , ▁b ending ▁the ▁DNA ▁and ▁separ ating ▁the ▁two ▁str ands . ▁The ▁N - term inal ▁domain ▁stabil izes ▁the ▁interaction ▁between ▁the ▁protein ▁and ▁the ▁cle aved ▁product , ▁thereby ▁protect ing ▁the ▁nick ▁from ▁DNA ▁lig ase ▁until ▁the ▁arrival