Cryo-EM Visualizes “9-1-1” Response to DNA Replication Errors

Researchers in Michigan and New York have uncovered new insights into the process by which cells recruit 911 DNA checkpoint clamp to fix errors in DNA replication. The mechanism is critical to maintaining health and preventing disease by ensuring genetic instructions are properly passed from one generation of cells to the next.

Billions of cells in the human body are replaced daily through cell division, a fundamental function that drives growth and facilitates maintenance of tissues such as skin and muscle. A central part of this system is DNA replication, in which our genetic instruction manual is carefully replicated to ensure each cell has an accurate copy. “DNA damage can have severe consequences, including cancer and other diseases. Because of this, our cells have a host of checks and balances to ensure DNA integrity,” says coauthor Huilin Li, Ph.D., of Van Andel Institute (VAI). 

DNA damage can result from mistakes in replication or through other factors that directly harm DNA, such as exposure to UV light from the sun or carcinogens such as tobacco smoke. When damage occurs, cells have emergency response systems to either stop replication until the problem can be repaired or to kill the cell, thus preventing the incorrect information from being passed on. This is where the 911 DNA checkpoint clamp comes in—when DNA damage is detected, the ring-shaped clamp is loaded on the DNA and transported to the site of the error. Once there, it sends a signal to halt cell division while also flagging other repair molecules to remove the damaged DNA and replace it with a corrected sequence.

Using VAI’s cryo-electron microscopes (cryo-EM), Li and colleagues at VAI and The Rockefeller University were able to visualize the molecular structures of the 911 checkpoint clamp at the atomic level. What they found was surprising. Rather than loading onto DNA from the 3’ end—like all other known DNA clamps—the 911 clamp loads onto DNA from the opposite, 5’ end.

This novel and unexpected finding is significant for understanding DNA replication and sets the stage for further studies in this area, according to the authors. “We hope these insights can be leveraged toward the development of new therapeutic strategies for diseases linked to DNA damage,” says Dr. Li.

The findings were published recently in Nature Structural & Molecular Biology.