Gratuitous induction.

We describe a novel mode of SOS induction, called gratuitous indirect induction, which is elicited when the maintenance of an intact lambda miniF introduced into a recipient was inhibited by a resident plasmid or by mutations in miniF that impaired partition or replication. Gratuitous induction required the presence of the lynA locus on miniF and was dependent on the host recA and lexA alleles. To account for gratuitous induction, we postulate that impairment of the normal co-regulation between partition and replication of miniF affects lynA functions whose disturbance leads to the production of an SOS signal.