Gabija restricts phage circularization and DNA replication

Anti-bacteriophage systems such as restriction-modification and CRISPR-Cas have DNA substrate specificity mechanisms that enable the identification of invaders. How Gabija, a highly prevalent nuclease-helicase antiphage system, limits phage replication while executing self- vs. non-self-discrimination remains unknown. Here, we show that phage-encoded DNA end-binding proteins that antagonize host RecBCD sensitize phages to Gabija. When targeting a temperate lambda-like phage in Pseudomonas aeruginosa, Gabija prevents phage genome circularization and subsequent replication. DNA end-binding complexes, including a phage exonuclease and a single-stranded DNA (ssDNA)-annealing protein or Gam_Mu dimers that prevent loading of the host repair complex RecBCD, are necessary and sufficient to license phage and plasmid sensitivity to Gabija. Mutant escape phages lacking these DNA end-binding proteins become protected from Gabija by RecBCD translocation activities. RecBCD activity on the bacterial genome, presumably whenever it is linearized, also prevents Gabija from targeting self-DNA. Therefore, we propose that Gabija antagonizes the circularization and replication of linear DNA devoid of RecBCD as a mechanism to identify and antagonize foreign invaders.