Members of the photolyase-cryptochrome superfamily (PCSF) utilise transient electron transfer (ET) for diverse reactions including light-driven DNA repair, and photo- and magnetoreception. As such, they represent a ubiquitous and central class of enzymes which has attracted an enormous amount of attention. Over the last years⁠, our group has specialised in the time-resolved crystallographic characterisation of these reactions, with one exception: repair of (6-4) Photoproduct (64PP) DNA lesions via (6-4)Photolyases. With the current proposal, we aim to employ Time-resolved serial oscillation crystallography (TR-SOX) techniques to structurally characterise this reaction for the first time.