Structure of the Escherichia coli Antitoxin MqsA (YgiT/b3021) Bound to Its Gene Promoter Reveals Extensive Domain

Bacterial cultures, especially biofilms, produce a small num-ber of persister cells, a genetically identical subpopulation of wild type cells that are metabolically dormant, exhibit multi-drug tolerance, and are highly enriched in bacterial toxins. The gene most highly up-regulated in Escherichia coli persisters is mqsR, a ribonuclease toxin that, along withmqsA, forms a novel toxinantitoxin (TA) system. Like all known TA systems, both the MqsRMqsA complex and MqsA alone regulate their own transcription. Despite the importance of TA systems in persistence and biofilms, very little is known about how TA modules, and antitoxins in particular, bind and recognize DNA at a molecular level. Here, we report the crystal structure of MqsA bound to a 26-bp fragment from themqsRA pro-moter. We show that MqsA binds DNA predominantly via its C-terminal helix-turn-helix domain, with direct binding o