Thymine (IMAGE) DOE/SLAC National Accelerator Laboratory Caption Thymine – the molecule in the foreground – is one of the four basic building blocks that make up the double helix of DNA. It's such a strong absorber of ultraviolet light that the UV in sunlight should deactivate it, yet this does not happen. In a study reported in Nature Communications, researchers used an X-ray laser at SLAC National Accelerator Laboratory to make detailed observations of a 'relaxation response' that protects these molecules, and the genetic information they encode, from UV damage. Credit Greg Stewart/SLAC Usage Restrictions Include credit License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.