Using a specialized protein, all bacteria are capable of rapidly and effectively repairing damage to their DNA from UV. However, this mutation frequency decline (Mfd) protein plays another role and causes mutations. A team1 involving scientists from CNRS, ENS-PSL and supported by Inserm has demonstrated and described this phenomenon. Better understanding of mutations opens up prospects in the fight against resistance to antibiotics and anti-cancer therapies. This study was published in PNAS on 5 April 2021.