Question

In dam methylation mismatch repair, what is the signal that causes MutH to join the Mut complex and to nick the unmethylated strand?

A. Recruitment of MutL

B. Recognition of the GATC site by MutS

C. DNA excision by exonuclease VII or I

D. UvrD helicase DNA unwinding

Answer 1

The signal that causes MutH to join the Mut complex and nick the unmethylated strand in dam methylation mismatch repair is recognition of the GATC site by MutS. MutS recognizes the mismatched nucleotides in the unmethylated strand and forms a complex with MutL and MutH. MutH then cleaves the unmethylated strand at the GATC site where the mismatch is located.

Step-by-step explanation:

The signal that causes MutH to join the Mut complex and nick the unmethylated strand in dam methylation mismatch repair is recognition of the GATC site by MutS.

In E. coli, DNA is hemimethylated, with the parental strand being methylated and the newly synthesized daughter strand being unmethylated. MutS protein recognizes the mismatched nucleotides in the unmethylated strand and forms a complex with MutL and MutH. MutH then cleaves the unmethylated strand at the GATC site where the mismatch is located.

This allows the exonuclease to remove the portion of the strand containing the incorrect nucleotide, and the gap is filled in by DNA pol III and ligase to complete the repair process.