Bacillus subtilis-phage phi 1 overcomes host-controlled restriction by producing BamNx inhibitor protein

Bacillus amyloliquefaciens N produces two restriction enzymes, BamNI and BamNx. Subtilis-phage phi 1 is strongly restricted by BamNx. We isolated phi 1 rH, a mutant of phage phi 1, which overcame the BamNx-restriction by producing inhibitor. This inhibitor inactivated BamNx specifically and reversibly. The inhibitor directly interacted with BamNx and the inactivation might be the result of formation of a binary complex. The inhibitory activity was sensitive to treatment with trypsin. The molecular weight of the inhibitor protein was estimated to be approximately 20,000 daltons by gel filtration.