Scientists have captured the most detailed structural images yet of the DNA repair process for a specific type of protein. The discovery may reveal ways to suppress the effects of BRCA1 and BRCA2 mutations, which increase the risk of breast, ovarian, and other cancers.
Previous studies have shown that a human protein called RAD52 performs DNA repair in cancer cells that lack the tumor-suppressing function of normal BRCA genes, allowing them to survive and reproduce, indicating that blocking RAD52 causes these cells to die.
However, blocking RAD52 requires a thorough understanding of its repair activities, which have been difficult to capture even with the most sophisticated techniques. So the researchers focused on its ancestor protein Mgm101 in yeast mitochondria and observed several key steps in its DNA repair process, called single-stranded DNA annealing.
A clearer understanding of how this family of proteins binds to DNA strands and rejoins them after being cut provides insight into drug targets that may halt processes in cancer cells that are enhanced by mutated BRCA genes.
“This is still a proposed mechanism. Just because we’re seeing a snapshot of these processes doesn’t mean we know all the details, but it gives us the best snapshot of the proteins that do this single-strand annealing,” said lead author Charles Bell, professor of biochemistry and pharmacology at The Ohio State University School of Medicine. “This focuses on our drug development strategy.”
The study was published today (April 27, 2026) in the journal. Nucleic acid researchdesignated this paper as a breakthrough article.
DNA strands are broken every day in every cell. That’s why proteins exist to repair breaks and keep cellular processes running smoothly. But repair must occur quickly, and because human proteins are often more complex than their ancestral proteins, even the most advanced imaging equipment cannot capture every step of the process.
Bell’s lab partnered on the study with a lab led by co-author Vicki Wysocki, professor emeritus at The Ohio State University and chair of the Department of Chemistry and Biochemistry at Georgia Tech. Wysocki’s lab specializes in native mass spectrometry and mass photometry, which use light to measure the mass of protein-DNA complexes.
These techniques showed that Mgm101 assembles from a monomer, or single copy of itself, to form a large multiunit molecular complex called a 19mer, a ring made up of 19 copies of the protein.
This ring exists as a template so that the first strand of DNA comes down and then the second strand emerges and begins to anneal to the first strand. ”
Vicki Wysocki, Professor Emeritus, Ohio State University
These findings were confirmed by Bell’s lab, which used cryoelectron microscopy to observe structures floating in solution and frozen in a thin layer of ice.
The high-resolution structure showed multiple stages of the process. The 19-mer ring has a single strand of DNA bound (substrate) and a second strand is positioned for annealing (double-stranded intermediate), after which the repaired DNA is released (B-type product), which appears as a classic double helix DNA formation.
“The high-resolution structure of RAD52 has been determined in single-stranded DNA, but not in the two pieces of DNA that we are trying to anneal,” Bell said. “Its role is to bind the single-stranded DNA and anneal it to its complementary sequence. It is captured structurally, but only in some states relevant to the reaction.
“Here, we get more states along the entire path from substrate to intermediate to product. And the double-stranded intermediate is a structure we’ve never seen before. When the protein binds to the first DNA around the ring, it’s bound only to the sugar-phosphate backbone, with the nucleotide bases facing up, fully exposed and separated, making it searchable. It’s elongated, fully unwound, and in a ring.”
Bell said that although the field does not know whether this mechanism takes place in one or two of the protein rings involved, these findings indicate that the process is managed by a single molecular complex, and therefore single-strand annealing is likely to be conserved. Sith mechanism.
The research team plans to try to capture the same steps in the DNA repair process using human RAD52, with a particular focus on double-stranded intermediates, and expand the role of mass spectrometry in determining how DNA binds to proteins.
This research was supported by the National Science Foundation and the National Institutes of Health. Cryo-EM data were collected at the Ohio State Electron Microscopy Analysis Center and processed using the Ohio Supercomputer Center.
Carter Wheat of Ohio State University and Jihao Qi, formerly of Ohio State and now at Georgia Tech, are co-lead authors of the study. Other co-authors include Mikdad Hussein, a student at Metro High School, and Katerina Zakharova, formerly of Ohio State University and now at CAS.
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Reference magazines:
connecticut wheat, Others. (2026) Mechanism of single-strand annealing from native mass spectrometry and cryo-EM structures of the RAD52 homolog Mgm101. Nucleic acid research. DOI: 10.1093/nar/gkag320. https://academic.oup.com/nar/article/doi/10.1093/nar/gkag320/8661651
