Fig. 1.
ToxNPa degrades RNAs and is inhibited by ToxIPa in vivo. (A) Schematic representation of ToxINPa with toxINPa genetic organization, processing of ToxIPa, and complex formation indicated. ToxNPa is shown in blue and ToxIPa in orange. (B) ToxNPa degrades the ompA transcript and is inhibited by ToxIPa in vivo. E. coli cells containing separately inducible ToxNPa-FLAG and ToxIPa plasmids were grown to log phase, and the effect of ToxNPa expression and subsequent coexpression of ToxIPa on ompA transcript levels was analyzed by Northern blot (Top). Expression of ToxIPa (Middle) and ToxNPa-FLAG (Bottom) also was assessed by Northern and Western blot, respectively. The symbols “+” and “−” represent induction and repression of ToxNPa or ToxIPa expression. Induction of a negative control is indicated by “0.” Because the RNA purification method used here excludes small RNAs, it was not possible to detect individual ToxIPa repeats. Note that because ToxNPa-FS expression did not affect growth, cells reached stationary phase and showed natural down-regulation of ompA transcription over the course of the experiment.