PARIS (for Phage Anti-Restriction-Induced System) is a novel anti-phage system. PARIS is found in 4% of prokaryotic genomes. It comprises an ATPase associated with a DUF4435 protein, which can be found either as a two-gene cassette or a single-gene fusion (1).
This system relies on an unknown [Abortive infection](/general_concepts/Abi) mechanism to trigger growth arrest upon sensing a phage-encoded protein (Ocr). Interestingly, the Ocr protein has been found to inhibit R-M systems and BREX systems, making PARIS a suitable defense mechanism against RM resistant and/or BREX resistant phages (1, 2, 3).
