What is mismatch repair and name a key protein complex involved in bacteria?

• A. It initiates replication at origin sites.
• B. It removes RNA primers.
• C. Mismatch repair corrects errors after replication; MutS and MutL (and MutH in some species) are key components.
• D. It synthesizes new DNA during replication.

Answer: (C)

Mismatch repair is a post-replication repair process that fixes base-pairing errors left after DNA has been synthesized. In bacteria, MutS recognizes a mismatch, MutL acts as a mediator, and MutH (in many species) creates a nick on the unmethylated, newly made strand near a GATC site to mark which strand to fix. Exonucleases remove the DNA from the nick through the mismatch, then DNA polymerase fills in the correct bases and DNA ligase seals the backbone. The other options describe different steps of replication—starting replication at the origin, removing RNA primers, or synthesizing new DNA—which are not mismatch repair.