Analysis of yeast MSH2-MSH6 suggests that the initiation of mismatch repair can be separated into discrete steps

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• The MSH2-MSH6 complex is crucial for DNA mismatch repair (MMR) in yeast, addressing base-pair and insertion/deletion mismatches.
• This complex binds to DNA mismatches and exhibits ATPase activity influenced by repairable mispairs.

Purpose of the Study:

• To investigate the initial stages of MMR by analyzing MSH2-MSH6 complexes with mutations in the MSH6 recognition domain.
• To determine if stable binding to a mismatch is sufficient for initiating downstream repair processes.

Main Methods:

• Analysis of MMR-defective MSH2-msh6 heterodimers with specific amino acid substitutions.
• Assessment of heterodimer binding affinity to mismatch and homoduplex DNA.
• Evaluation of MSH2-MSH6 ATPase activity and MLH1-PMS1 complex recruitment.

Main Results:

• Mutant MSH2-msh6 heterodimers showed defects in stable complex formation with mismatch substrates.
• MSH2-msh6-340 bound homoduplex DNA similarly to the wild-type complex, indicating binding affinity is not solely dependent on mismatch recognition.
• Stable binding to a specific palindromic insertion mismatch did not modulate ATPase activity or recruit MLH1-PMS1, suggesting a requirement for further steps.

Conclusions:

• Early MMR stages involve distinct steps: initial recognition, stable binding, and subsequent recruitment of downstream factors.
• Stable DNA mismatch binding by MSH2-MSH6 is necessary but not sufficient for initiating the MMR pathway.
• The findings provide a refined model for the sequential events in DNA mismatch repair initiation.