In bacteria, which protein complex is a key component of mismatch repair?

In bacteria, which protein complex is a key component of mismatch repair?

• A. RecA
• B. MutS and MutL (MutH in some species)
• C. DNA polymerase I
• D. Primase

Answer: (B)

Mismatch repair in bacteria hinges on the MutS–MutL complex, with MutH acting on the strand in many species. MutS scans DNA and recognizes a base-pair mismatch or small insertion/deletion. MutL serves as a coordinator, linking MutS to the rest of the repair machinery. In the classic system, MutH introduces a nick on the unmethylated daughter strand near a GATC site, which allows exonucleases to remove the error-containing segment. DNA polymerase III then fills the gap and DNA ligase seals the nick. Some bacteria lack MutH and use alternative nicking enzymes, but the MutS–MutL core is still essential for recognizing errors and orchestrating repair. Other proteins here have different roles—RecA in recombination and SOS response, DNA polymerase I mainly in base excision repair and processing DNA gaps, and primase for starting RNA primers during replication—so they aren’t the central components of mismatch repair.

Mismatch repair in bacteria hinges on the MutS–MutL complex, with MutH acting on the strand in many species. MutS scans DNA and recognizes a base-pair mismatch or small insertion/deletion. MutL serves as a coordinator, linking MutS to the rest of the repair machinery. In the classic system, MutH introduces a nick on the unmethylated daughter strand near a GATC site, which allows exonucleases to remove the error-containing segment. DNA polymerase III then fills the gap and DNA ligase seals the nick. Some bacteria lack MutH and use alternative nicking enzymes, but the MutS–MutL core is still essential for recognizing errors and orchestrating repair. Other proteins here have different roles—RecA in recombination and SOS response, DNA polymerase I mainly in base excision repair and processing DNA gaps, and primase for starting RNA primers during replication—so they aren’t the central components of mismatch repair.