The ClpX protease is essential for removing the CI master repressor and completing prophage induction in Staphylococcus aureus

Abstract Bacteriophages (phages) are the predominant biological entities on the planet and play an important role in the spread of bacterial virulence, pathogenicity, and antimicrobial resistance. After infection, temperate phages can integrate in the bacterial chromosome thanks to the expression of the prophage-encoded CI master repressor. Upon SOS induction, and promoted by RecA*, CI auto-cleaves generating two fragments, one containing the N-terminal domain (NTD), which retains strong DNA-binding capacity, and other corresponding to the C-terminal part of the protein. However, it is unknown how the CI NTD is removed, a process that is essential to allow prophage induction. Here we identify for the first time that the specific interaction of the ClpX protease with the CI NTD repressor fragment is essential and sufficient for prophage activation after SOS-mediated CI autocleavage, defining the final stage in the prophage induction cascade. Our results provide unexpected roles for the bacterial protease ClpX in phage biology.