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DNA in a cell is under constant stress from environmental factors, such as ultraviolet light, or from damage caused by the replication process. These sources of stress can cause breaks in the genome, which if left unrepaired can lead to cancer or cell death. One of the most accurate ways to repair a broken fragment of DNA is through recombination – whereby an undamaged copy of the sequence is located in another DNA molecule and used as a template to replace the missing fragment.
DNA recombination is regulated by more than a dozen proteins that help recruit the enzyme RAD51 to sites of DNA damage, and trigger its search for complementary sequences of DNA. A molecule known as PALB2 binds to these DNA repair proteins and coordinates their activity. If PALB2, or these other proteins become mutated, this can increase the risk cancerous growths in various tissues, including the breasts and ovaries. Having a better understanding of how this group of proteins control the repair process could therefore improve prognosis and advance cancer treatments.
Now, Deveryshetty et al. have discovered a new and unexpected role for PALB2 within the recombination pathway. As well as binding to other repair proteins, PALB2 interacts directly with DNA, and this interaction was found to be an important part of the repair process. Even in the absence of RAD51, PALB2 was still able to recombine short fragments of DNA sequence. PALB2 achieves this by initiating recombination using single strands of DNA or a DNA-like molecule known as RNA. This latter property may be particularly important if the molecular machines needed to replicate DNA and synthesize RNA collide on the same DNA molecule.
This new role for PALB2 could lead to the discovery of other DNA repair mechanisms, and could be used to predict which PALB2 mutations are more likely to cause cancer. Patients who are at greater risk of cancer could then be treated with more advanced therapies, in order to increase their chances of recovery.