Figure 35.7 Mismatch repair. DNA mismatch repair in E. coli is initiated by the interplay of MutS, MutL, and MutH proteins. A G–T mismatch is recognized by MutS. MutL binds to MutS and activates the MutH nuclease. MutH cleaves the backbone in the vicinity of the mismatch. A segment of the DNA strand containing the erroneous T is removed by exonuclease I and synthesized anew by DNA polymerase III.