Visualization of mismatch repair in bacterial cells

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• DNA replication fidelity is crucial for preventing mutations.
• The mismatch repair (MMR) system corrects errors missed by DNA polymerase.
• Understanding MMR protein localization provides insights into DNA repair mechanisms.

Purpose of the Study:

• To determine the subcellular localization of key mismatch repair proteins, MutS and MutL, in living Bacillus subtilis cells.
• To investigate the dynamics of MutS and MutL localization in response to DNA mismatches and replication.
• To elucidate the spatiotemporal relationship between MMR proteins and the replication machinery.

Main Methods:

• Green Fluorescent Protein (GFP) tagging of MutS and MutL proteins.
• Live-cell imaging microscopy in Bacillus subtilis.
• Induction of DNA mismatches using 2-aminopurine.
• Colocalization analysis with DNA polymerase foci.

Main Results:

• MutS-GFP localized throughout the chromosome and formed distinct foci in some cells.
• MutL-GFP foci formation was dependent on the presence of MutS.
• Inducing mismatches increased the proportion of cells exhibiting MutS and MutL foci in a replication-dependent manner.
• Approximately 50% of MutS foci colocalized with DNA polymerase foci.

Conclusions:

• MutS is broadly associated with the Bacillus subtilis chromosome, ready to detect mismatches.
• Mismatch repair foci assemble at newly formed mismatches emerging from DNA polymerase.
• Continuing DNA replication appears to displace these MMR foci from the replication fork.