Dual daughter strand incision is processive and increases the efficiency of DNA mismatch repair

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• DNA mismatch repair (MMR) corrects replication errors.
• In E. coli, MutS, MutL, and MutH proteins initiate MMR by nicking DNA at GATC sites.
• MMR efficiency is influenced by GATC site distribution.

Purpose of the Study:

• To quantitatively assess how strand incision affects DNA unwinding and excision during MMR.
• To elucidate the roles of specific MMR proteins (MutS, MutL, MutH) in the repair process.
• To develop a general model for MMR in prokaryotes and eukaryotes.

Main Methods:

• Quantitative analysis of strand incision effects on MMR activity.
• Studying the processivity of MMR complex interactions with GATC sites.
• Comparing repair efficiency on substrates with varying nick configurations.

Main Results:

• The distance to GATC sites did not affect strand incision rates; more sites slightly increased incision.
• A single MMR complex incised two GATC sites processively, with distinct roles for MutS, MutL, and MutH.
• Two nicks flanking the mismatch significantly enhanced unwinding and excision compared to single or same-side nicks.
• Human MutLα also increased repair efficiency with multiple nicks.

Conclusions:

• MMR efficiency is significantly improved by multiple nicks flanking the DNA mismatch.
• A unified model for MMR is proposed, highlighting the role of multiple nicks in both prokaryotic and eukaryotic systems.
• Mismatch-activated complexes orchestrate efficient repair through strategic DNA nicking.