Final answer:
In mismatch repair, the new strand which contains the mismatch, such as G bonding with T, undergoes excision and repair, guided by the parental strand's methylation pattern. The repair involves specific enzymes such as MutS, MutL, and MutH, which recognize and remove the mismatched nucleotides before DNA polymerase III and DNA ligase restore the correct sequence.
Step-by-step explanation:
During mismatch repair, the enzymes involved must be able to distinguish between the original (parental) strand and the newly synthesized (daughter) strand. This is important because the newly synthesized strand is the one that will undergo excision and repair since it is the one that may contain the mismatched bases such as guanine (G) bonding with thymine (T). In E. coli, this differentiation is made by recognizing the methylation pattern on the DNA strands. The parental strand is methylated, while the newly synthesized daughter strand is not yet fully methylated. The mismatch repair proteins, including MutS, MutL, and MutH, bind to the hemimethylated site of the DNA where the mismatch is recognized. MutH then specifically cleaves the unmethylated strand (the new strand), which allows an exonuclease to remove a section of this strand, including the mismatched nucleotide. The gap is then filled with the correct nucleotides by DNA polymerase III, and finally, the strand is sealed by DNA ligase.