Gabija restricts phages that antagonize a conserved host DNA repair complex

Anti-bacteriophage systems like restriction-modification and CRISPR-Cas have DNA substrate specificity mechanisms that enable identification of invaders. How Gabija, a highly prevalent nuclease-helicase anti-phage system, executes self- vs. non-self-discrimination remains unknown. Here, we propose that phage-encoded DNA end-binding proteins that antagonize host RecBCD sensitize phages to Gabija. When targeting temperate phage D3 in Pseudomonas aeruginosa, Gabija functions early by preventing phage genome circularization in a non-abortive manner. Phage and plasmid DNA-end sensitivity to Gabija is licensed by a phage exonuclease and ssDNA-annealing protein. Unrelated F8 and JBD30 phages are sensitized to Gabija by Gam_Mu, a distinct DNA end-binding protein that antagonizes loading of the host repair complex RecBCD. Escape phages lacking these end-binding proteins become protected from Gabija by RecBCD activities, which also prevent Gabija from targeting self-DNA. Therefore, we propose that Gabija antagonizes circularization of linear DNA devoid of RecBCD as a mechanism to identify foreign invaders.