Prokaryotic Gabija complex senses and executes nucleotide depletion and DNA cleavage for antiviral defense

ABSTRACT The Gabija antiviral system consists of the GajA and GajB proteins. We previously revealed that GajA is a DNA nicking endonuclease. In this work, we found that the DNA binding of GajA is strictly inhibited by NTP. Furthermore, the antiviral defense of GajA requires the assistance from GajB, which senses DNA termini produced from the DNA nicking by GajA to hydrolyze (d)A/(d)GTP. The synergy between the DNA cleavage by GajA and the nucleotide hydrolysis by GajB results in an efficient abortive infection defense against virulent bacteriophages. GajA binds to GajB to form stable complexes in vivo and in vitro . However, a functional Gabija complex requires the molecular ratio between GajB and GajA below 1:1. Through (i) sequential sensing and executing the nucleotide depletion and DNA cleavage to cause a cascade suicide effect and (ii) stoichiometry regulation of the DNA/nucleotide processing complex, the Gabija system exhibits a unique mechanism distinct from other known prokaryotic antiviral systems.