Yes, Mismatch Endonuclease I will cleave a substrate with sequential T:T, G:G or T:G DNA mismatches. However, Mismatch Endonuclease I cannot cleave a bulged DNA substrate with multiple (>2) consecutive mismatches. Additionally, if your DNA contains multiple sequential mismatches, Mismatch Endonuclease I will preferentially cleave at a T:T mismatch over a G:G or T:G mismatch.