Against the harmful effects of sunlight on DNA, nature has developed some defenses. Incoming UV photons have enough energy to trigger consecutive DNA base pairs to distort the well-known double-helix geometry and form what are called cyclobutane pyrimidine dimers (CPDs), which disrupt DNA replication and cause skin cancer. In response, some organisms—though not humans—have enzymes called photolyases. Powered by visible light, they repair the damage through a series of reactions on the CPDs.
Thanks to spectroscopy findings and theoretical studies, scientists have known about the DNA repair process for the past 30 years. But the exact mechanism and the structure of the chemical species at play have been difficult to visualize. Among the challenges is that the damaged DNA and the photolyase must be acquired in dark, oxygen-free conditions. And the repair process operates at atomic resolution over time scales of picoseconds to microseconds.
Now the repair has been caught in action. Two separate teams—Manuel Maestre-Reyna of Academia Sinica and National Taiwan University in Taipei and colleagues and Nina-Eleni Christou at the German Electron Synchrotron in Hamburg and colleagues—used a technique known as time-resolved serial femtosecond crystallography to obtain snapshots of the process and make a timeline of its key events.
To read more, click here.