Homologous Recombination Mechanisms in Bacterial Systems

Homologous recombination in bacteria is a fundamental process for the repair of DNA double-strand breaks, the resolution of stalled or collapsed replication forks and the integration of foreign DNA during horizontal gene transfer. Central to this pathway is the RecA recombinase, which polymerises on single-stranded DNA to form a nucleoprotein filament that searches for homologous duplex sequences and catalyses strand invasion to establish a displacement loop (D-loop). Accessory factors—including single-strand binding proteins, mediators and modulators—fine-tune RecA filament dynamics, regulate branch migration and ensure fidelity. Branch migration proteins such as RuvAB and RadA/Sms drive the extension of heteroduplex DNA, while resolvases cleave Holliday junctions to complete strand exchange. This orchestrated series of events preserves genomic integrity under conditions of genotoxic stress, facilitates adaptive evolution, and underlies key biotechnological applications such as genome editing and microbial engineering.

Research from Nature Portfolio

Recent structural and functional studies have reshaped our understanding of single-strand annealing proteins (SSAPs) across domains. Cryo-electron microscopy of prokaryotic SSAPs reveals clear architectural parallels with the eukaryotic Rad52 core, confirming an ancient evolutionary link and suggesting conserved mechanisms of homology recognition and DNA annealing. High-resolution structures capture the mode of DNA binding and oligomeric transitions that clamp strands to secure sequence identity. Complementary work on bacterial RadA uncovers a hexameric DnaB-type helicase that cooperates with RecA to extend D-loops bidirectionally. Biochemical assays and structural models demonstrate how RecA recruits RadA hexamers to opposing D-loop boundaries, driving branch migration and facilitating long-range strand assimilation during natural transformation. Single-molecule tracking in live cells further highlights the rapid assembly and dynamic behaviour of repair centres, revealing that factors such as RecN, RecO and RecJ transition between diffusive and DNA-scanning modes to orchestrate presynaptic preparation of double-strand breaks throughout the chromosome.

Homologous Recombination Mechanisms in Bacterial Systems publication trend

The graph below shows the total number of articles in homologous recombination mechanisms in bacterial systems across all publications each year (not limited to Nature Index journals).

Technical terms

Homologous recombination: A DNA repair process using an undamaged homologous template to accurately restore broken or stalled DNA.

RecA recombinase: A protein that polymerises on single-stranded DNA to form a filament capable of searching for and invading homologous duplex DNA.

Single-strand annealing protein (SSAP): A factor that binds complementary single strands and promotes annealing, often forming oligomeric clamps to stabilise nascent duplexes.

D-loop: A displacement loop formed when an invading single strand pairs with its homologous region in duplex DNA, displacing one original strand.

Branch migration: The process by which the crossover point between paired DNA strands moves along the duplex, extending the region of heteroduplex DNA.

Holliday junction: A four-way DNA intermediate formed during strand exchange that must be resolved to complete recombination.

Replication fork: The Y-shaped structure where parental DNA strands are unwound and copied during replication; prone to stalling under stress.

References

1. Processing of stalled replication forks in Bacillus subtilis. FEMS Microbiology Reviews (2023).
2. The Rad52 SSAP superfamily and new insight into homologous recombination. Communications Biology (2023).
3. Bacillus subtilis RadA/Sms-Mediated Nascent Lagging-Strand Unwinding at Stalled or Reversed Forks Is a Two-Step Process: RadA/Sms Assists RecA Nucleation, and RecA Loads RadA/Sms. International Journal of Molecular Sciences (2023).
4. Bacterial RadA is a DnaB-type helicase interacting with RecA to promote bidirectional D-loop extension. Nature Communications (2017).
5. Single molecule tracking reveals spatio-temporal dynamics of bacterial DNA repair centres. Scientific Reports (2018).