Fig. 2.

The bottom-surface mutant (FtsZ^L272E) is dominant negative with substoichiometric toxicity. Plasmid pSD334 (P_tac::ftsZ) or derivatives containing different ftsZ alleles were transformed into strain JS238, and transformants were tested for toxicity. A 3-µL aliquot from each 10-fold serial dilution was spotted onto LB plates with chloramphenicol and IPTG and incubated at 37 °C overnight before imaging. (B) Cultures of some of the strains from A were induced with 30 μM IPTG for 2 h, and cells were photographed. (Scale bar: 5 µm.) (C) JS238-containing derivatives of pSD334 expressing ftsZ^L272E or ftsZ^360(L272E) were induced with the indicated concentration of IPTG for 2 h, and a Western blot was performed to assess the level of the induced proteins. ZipA was blotted as a control. The sample from the 20-μM induction of ftsZ^360(L272E) was serially diluted as indicated to assess the induced amount of FtsZ^360(L272E) relative to the endogenous level of FtsZ. The level of FtsZ in the 1/10 dilution was about the level of FtsZ^360(L272E) in the undiluted sample.