Inversion/dimerization of plasmids mediated by inverted repeats

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Recombination is crucial for DNA repair and genome stability.
• Previous studies focused on RecA-dependent recombination in bacterial genomes.
• Inverted repeats on plasmids were known to undergo recombination, but the mechanism was unclear.

Purpose of the Study:

• To investigate the mechanism of recombination between inverted repeats on plasmids.
• To determine the role of known recombination enzymes in this process.
• To elucidate the factors influencing the efficiency of this recombination event.

Main Methods:

• Plasmid construction with varying inverted repeat sequences and mismatch incorporation.
• Genetic analysis using single and double mutants of recombination pathways (e.g., RuvABC, RecG/RusA).
• Analysis of recombination products using sequencing to determine the mechanism.

Main Results:

• Plasmid recombination between inverted repeats is highly efficient and RecA-independent.
• The recombination product is exclusively a head-to-head inverted dimer.
• Recombination efficiency is dramatically reduced by mismatches within repeats, and DNA mismatch repair genes (dam, mutH, mutL) influence this.
• Known Holliday junction resolution systems are not essential for this recombination.
• Most products do not involve crossing-over, suggesting a non-reciprocal mechanism.

Conclusions:

• Plasmid recombination via inverted repeats is a distinct, RecA-independent pathway.
• The process likely involves heteroduplex formation and is sensitive to DNA repair pathways.
• A model involving lagging strand polymerase blockage by a hairpin is proposed.