DNA repair proteins constantly bind and let go of DNA damage sites. Luijsterburg et al. discover how these seemingly fickle proteins get the job done.
During nucleotide excision repair, ten proteins collaborate to fix DNA, handling separate steps such as recognizing damage, unwinding the DNA, snipping out the marred section, and installing replacement nucleotides. Instead of assembling into a complex beforehand, the proteins come together at the site of damage. So how do the proteins make repairs if they adhere to the complex only for a short time?
Luijsterburg et al. tracked seven of the proteins in cells zapped by ultraviolet light. Repair complexes stuck to DNA for hours, but individual proteins only adhered for tens of seconds. This isn't contradictory, the researchers say. Proteins randomly attach and detach until the right combination is present to catalyze the first repair step. Reshuffling continues until a complex convenes to catalyze the next step, and so on. The result challenges previous findings that complexes assemble in sequence, with each protein staying on after its task is complete.
Luijsterburg et al.'s model suggests a benefit for quick-release proteins. They make it easier to abort the process if repair starts on undamaged DNA, a mistake that can result in mutations. Next up, the researchers say, is determining whether similar mechanisms occur in other processes involving unstable complexes, such as DNA replication and transcription.
