Homologous recombination requires the a nick or break in dsDNA, invasion of a homologous dsDNA molecule by a ssDNA end, pairing of homologous sequences, branch migration to form a Holliday junction, and isomerization of the flanking sequences. Early models proposed that only a limited amount of DNA synthesis is required for recombination. An cartoon of this basic model is shown below.
That model led to a tremendous number of insightful experiments on the mechanism of recombination. However, it became clear that double-strand breaks often initiate genetic recombination. This led to an updated model for the initiation of recombination shown below.
The final step of recombination involves the resolution of the Holliday junctions. An example showing a single Holliday junction is shown below.
Subsequently, evidence that recombination plays an essential role in the repair of damaged DNA replication forks established an intimate relationship between recombination and DNA synthesis.
This led to a recent model for recombination that leads to DNA replication forks, demanding DNA synthesis to complete the replication process. Research over the last few years indicates that this is probably how much recombination occurs in bacteria.
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Last modified October 12, 2003