Which of the following statements about methyl-directed mismatch repair in E. co

Question

Which of the following statements about methyl-directed mismatch repair in E. coli is FALSE?

The MutL-MutS complex scans the DNA for hemi-methylated GATC sequences.

Hemi-methylated GATC sequences allow MutH to “mark” the newly synthesized strand.

It is possible only for a short while after replication because GATC sequences become fully-methylated by the Dam methyltransferase.

MutH is an endonuclease that is specific for hemi-methylated GATC sequences.

The MutL-MutS complex binds specifically to mismatches.

The MutL-MutS complex scans the DNA for hemi-methylated GATC sequences.

Explanation / Answer

MutL forms a dimer and binds MutS. Then the MutS-MutL complex binds to the mutated DNA. So, statement ‘e’ is correct. But statement ‘a’ is incorrect. The complex does not scan the DNA for hemi-methylated GATC sequence.

MutH which binds at hemi-methylated strands along the daughter DNA; so, statement ‘b’ is correct. It is MutH which marks the daughter strands.

Statement ‘c’ is also correct. Dam methylase methylate the DNA shortly after replication. So, only for a small period this process is possible.

Statement ‘d’ is also correct. MutH is an endonuclease. It produces a nick in DNA at the hemi-methylated site.

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