Final answer:
Methylation acts as a signal in methyl-directed mismatch repair, allowing repair enzymes to recognize incorrect nucleotides in the DNA strands and replace them with the correct bases.
Step-by-step explanation:
Methylation plays a crucial role in methyl-directed mismatch repair. In this process, the DNA is hemimethylated, meaning that the parental strand is methylated while the newly synthesized daughter strand is not. The methylation acts as a signal for the repair enzymes to recognize the incorrect nucleotide in the nonmethylated strand. The repair enzymes then excise the incorrect nucleotide and replace it with the correct base.