Final answer:
DNA methyltransferase is the enzyme that recognizes methylated CG sequences in DNA and catalyzes methylation of the complementary strand post-replication, playing a key role in mismatch repair by differentiating parental and daughter strands.
Step-by-step explanation:
The enzyme that recognizes already methylated CG sequences in DNA and catalyzes the methylation of the corresponding CGs in the complementary strand is known as DNA methyltransferase. In the process of mismatch repair, particularly in E. coli, this enzyme acts after DNA replication to maintain the epigenetic marks of the parental DNA strand. Methylation is crucial as it helps to differentiate between the newly synthesized DNA strand, which lacks methylation, and the parental strand. This allows mismatch repair mechanisms to correct errors by targeting the non-methylated, newly synthesized DNA strand for error checking and repair.
Immediately following DNA replication, methylated parental strands serve as a guide for mismatch repair enzymes to identify and correct any replication errors in the new, non-methylated daughter strands. Methylation status thereby serves as a mark of the template strand, ensuring the fidelity of the replication process. It is important to note that this process is different in prokaryotes and eukaryotes due to variations in their methylation and mismatch repair mechanisms.