Restriction and modification in Bacillus subtilis: inducibility of a DNA methylating activity in nonmodifying cells

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Abstract
The nonrestricting/nonmodifying strain B. subtilis 222 (r-m-) can be induced to synthesize a DNA-modifying activity upon treatment with either mitomycin C (MC) or UV light. Infection of MC-pretreated 222 cells with unmodified SPP1 phage yielded about 3% modified phage that were resistant to restriction in B. subtilis R (r+m+). The induced modifying activity cause the production of a small fraction of fully modified phage in minority class of MC-treated host cells. The MC-pretreated host cells contained a DNA cytosine methylating activity; both bacterial and phage DNA had elevated levels of 5-methylcytosine. The MC-induced methylation of SPP1 DNA took place at the recognition nucleotide sequences of restriction endonuclease R from B. subtilis R. Crude extracts of MC-pretreated 222 cells enhanced DNA methyltransferase activities, with a substrate specificity similar to that found in modification enzymes present in (constitutively) modifying strains.

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