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

Summary A Bsu168-specific restriction deficient (r₁₆₈^-) mutant of Bacillus subtilis Marburg 168 was transformed to be BsuR-specific restriction proficient (r_R⁺) with B. subtilis R DNA as efficiently as the Bsu168-specific restriction proficient (r₁₆₈⁺) parental strain (hsrM⁺, hsdR^-).We constructed r_R⁺m_R⁺r₁₆₈⁺m₁₆₈⁺strain (ISMR 4), r_R⁺m_R⁺r₁₆₈^-m₁₆₈⁺strain (ISR 11) and r_R⁺m_R⁺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 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 r_R⁺m_R⁺transformant of r₁₆₈⁺m₁₆₈⁺strain B. subtilis 168.