When chromosomes experience double-strand breaks resulting from oxidation, ionizing radiation, replication errors and certain metabolic products in cells, they utilize their genetically similar chromosomes to patch the gaps via a mechanism that involves both ends of the broken molecules. To repair a broken chromosome that lost one end, a unique configuration of the DNA replication machinery is deployed as a desperation strategy to allow cells to survive, the researchers discovered.
The collaborative work of graduate students working under Anna Malkova Ph.D., associate professor of biology at Indiana University-Purdue University Indianapolis (IUPUI) and Kirill Lobachev, Ph.D., associate professor of biology at the Georgia Institute of Technology, was critical in the advancement of the project.
The group's research will be published online this week in the Nature
journal, with two graduate students (Natalie Saini from the Georgia Institute of Technology and Sreejith Ramakrishnan from the School of Science at IUPUI) as first authors. Other collaborators include Dr. James Haber, Ph.D., Brandeis University, and Grzegorz Ira, Ph.D., Baylor College of Medicine.
"Previously, we have shown that the rate of mutations introduced by break-induced replication is 1000 times higher as compared to the normal way that DNA is made naturally, but we never understood why," Malkova said.
The latest research reveals a mode of replication that can operate in non-dividing cells—the state of most of the body's cells—making this kind of replication a potential route for cancer formation.
"Potentially, this is a textbook discovery," Lobachev said.
The two labs used cutting-edge analysis techniques and equipment available at only a handful of facilities around the world. This allowed the researchers to see inside yeast cells and freeze the break-induced DNA repair process at different times. They found this mode of DNA repair doesn't rely on the traditional replication fork — a Y-shaped region of a replicating DNA molecule — but instead uses a bubble-like structure to synthesize long stretches of missing DNA. This bubble structure copies DNA in a manner not seen before in eukaryotic cells and leads to conservative DNA synthesis that promotes highly increased mutagenesis.