Host-controlled modification and restriction in Bacillus subtilis: Bsu 168-system and BsuR-system in B. subtilis 168.

A Bsu168-specific restriction deficient (r168-) mutant of Bacillus subtilis Marburg 168 was transformed to be BsuR-specific restriction proficient (rR+) with B. subtilis R DNA as efficiently as the Bsu 168-specific restriction proficient (r168+) parental strain (hsrM+, hsdR-). We constructed rR+ mR+ r168+ m168+ strain (ISMR 4), rR+ mR+ r168- m168+ strain (ISR 11) and rR+ mR+ r168- m168- strain (ISR 6) from strain 101 (r168+ m168+), strain 1012 (r168- m168+) and strain RM125 (r168- m168-), respectively by transformation with B. subtilis R DNA, and tested their restriction and modification activities on phage phi 105C. The results show that the sites recognized by Bsu168-specific restriction and modification enzymes and the sites recognized by BsuR-specific ones are not overlapping. We conclude that the Bsu168-modification and restriction system and the BsuR-modification and restriction system are controlled independently by two distinct sets of genes in the rR+ mR+ transformant of r168+ m168+ strain B. subtilis 168.