98.7 % of sunlight UV that reaches the Earth’s surface is UVA. But, this wavelength range has been overlooked in studies of how UV light damages DNA leading to potentially carcinogenic mutations. Understanding how different wavelengths of UV induce different photochemistry in the genetic material is important to understanding the mechanism of damage.

Researchers in France have, apparently for the first time, looked at how UVA affects DNA. UVB and UVC have been the exclusive focus of such research until now. Their results show that cyclobutane dimers readily form upon base pairing under UVA, a pre-mutagenic change that blocks DNA replication.

• Base Pairing Enhances Fluorescence and Favors Cyclobutane Dimer Formation Induced upon Absorption of UVA Radiation by DNA,
  Akos Banyasz, Ignacio Vay, Pascale Changenet-Barret, Thomas Gustavsson, Thierry Douki, Dimitra Markovitsi,
  J. Am. Chem. Soc. 2011, online.
  DOI: 10.1021/ja110879m