Telomeres play important roles in cell division, carcinogenesis and aging. They can be affected by oxidative damage, which was thought to be principally induced by molecules derived from metabolism or linked to the environment (i.e. pollution, drugs). 

And yet, telomere DNA turns out to be capable of absorbing UVB photons that have an energy (4.2 eV) well below the direct ionization threshold (6 eV), with a probability comparable to that of conventional photo-induced damage (on the order of several thousandths). This excitation could be at the source of the oxidative damage, as shown by the formation of a marker (8-oxo-guanine).

The detail of the mechanisms involved can be experimentally revealed by specifically irradiating telomeres whose ends are folded in a four-stranded structure (G-quadruplexes) with a UV laser at 295 nanometers (4.2 eV). Using electron spectroscopy and time-resolved absorption spectroscopy coupled with quantum chemistry calculations, the researchers were able to identify and measure the lifetime of the radicals formed. The analysis of the process demonstrates the initial formation of a cation (positively charged) that is neutralized either by rapidly losing an external proton (< 20 µs), or by losing an inner proton over longer times (5-180 ms).

This work was conducted within the framework of the ANR Ophid project, which is coordinated by the Iramis (in collaboration with the Inac) and an Alembert Chair (Idex Université Paris-Saclay) awarded to Roberto Improta at the Iramis.