Supporting Protocols and References Three Dimensional Structure of the MqsR:MqsA Complex: a Novel TA Pair comprised of a Toxin Homologous to RelE and an Antitoxin with Unique Properties

BW25113/MG1655 growth assays The bacterial strains and plasmids used in this study are listed in Table S1. Growth experiments with E. coli strain BW25113 and MG1655 were conducted in LB medium at 37°C. Growth experiments were monitored using pBS(Kan)-based plasmids [1]. To construct pBS(Kan)-based plasmids for producing MqsR, MqsA-F, and MqsR-MqsA-F from a lac promoter, the fragments from genomic DNA were amplified by PCR (Table S2) and directionally cloned into pBS(Kan). The toxicity of selected proteins was investigated using pBS(Kan) plasmids with 1 mM IPTG added upon inoculation. Growth measured using culture optical density at 600 nm (OD600). Cell viability (CFU) measured by diluting cells from 10 to 10 via 10-fold serial dilution steps into 0.85% NaCl solution and applying them as 10 μL drops on LB agar with kanamycin or chloramphenicol [2]. Two independent cultures were used for each strain. Data shown (Figs. 1, S1) represents the average of the two measurements with the standard deviation shown as error bars.