Toxin-antitoxin systems are subject to both auto- and cross-regulation. Cognate regulatory interactions are in red and non-cognate interactions are in blue. According to the established model, cognate antitoxin and toxin, which are encoded by co-transcribed genes, form a tight complex and antitoxin inhibits the toxin through direct protein-protein interaction. Antitoxin, both alone and in complex with the toxin, binds to the operator DNA and auto-represses transcription of the TA operon. Free toxin in excess disrupts this DNA-protein interaction and induces transcriptional de-repression. We show that transcription of TA genes can be induced also by non-cognate toxins. Moreover, cleavage of the TA mRNA by both cognate and non-cognate toxins results in accumulation of the toxin-encoding mRNA fragments. Translation of these fragments can lead to accumulation of free toxin.
Kasari et al. BMC Microbiology 2013 13:45 doi:10.1186/1471-2180-13-45