RecE-dependent lysogenic induction in the absence of repressor in Bacillus subtilis non-complementing diploids

The RecE protein of Bacillus subtilis, known to be required for induction of the SOS response and of phi 105 prophage, was shown to be involved in mitomycin C induction of B. subtilis diploid lysogens carrying a silent phi 105 prophage in their unexpressed chromosome. These stable non-complementing diploid lysogens, formed by protoplast fusion and regeneration, did not synthesize repressor, so that the induction observed must have resulted from RecE-dependent activation of the prophage rather than from RecE-dependent inactivation of repressor. Mitomycin C treatment does not induce permanent expression of the silent chromosome, so the activation seems to be temporary, perhaps reflecting the action of an SOS function under RecE control.