Spatial coupling between DNA replication and mismatch repair in Caulobacter crescentus.

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• DNA mismatch repair (MMR) is crucial for correcting DNA replication errors across diverse organisms.
• In bacteria, MutS and MutL proteins initiate MMR, with MutS identifying mismatches and MutL nicking the DNA strand.
• Rifampicin resistance serves as a selectable marker to study the efficiency of MMR in preventing mutations.

Purpose of the Study:

• To investigate the role and mechanism of the DNA mismatch repair (MMR) system in the Alphaproteobacterium Caulobacter crescentus.
• To elucidate the spatiotemporal association of MMR proteins (MutS and MutL) with the replication machinery (replisome).
• To propose a model for MMR initiation and execution in C. crescentus, highlighting the distinct roles of MutS and MutL.

Main Methods:

• Utilized fluorescently-tagged MutS and MutL proteins for live-cell microscopy in Caulobacter crescentus.
• Performed quantitative analysis of MMR's impact on the emergence of rifampicin resistance.
• Employed cell cycle analysis to track the association of MMR proteins with the replisome during DNA replication.

Main Results:

• MMR significantly reduces the occurrence of rifampicin resistance by over 100-fold in C. crescentus.
• MutS exhibits stable association with the replisome throughout S-phase, while MutL shows dynamic association.
• Spatial association of MutL with the replisome is essential for MMR, suggesting a model involving the β-sliding clamp.
• MutS-replisome association is dispensable under standard growth conditions, indicating flexibility in MMR initiation.

Conclusions:

• MMR is a highly efficient system in C. crescentus, preventing a substantial mutation rate.
• A model is proposed where the replication fork, potentially licensed by the β-sliding clamp, recruits MutL for endonuclease activity.
• The dynamic association of MMR proteins with the replisome may be a conserved mechanism in Alphaproteobacteria for efficient and accurate DNA repair.