Table 2.

Effect of zipA plasmids on division of wild-type cellsa

PlasmidInducible proteinIPTG concnb (μM)Relative protein concncDivision blockd
pMLB1113ΔHeNone>500
pDB322ZipA257+
pCH49ZipA-H1006+
pCH182ZipA(1–302)-H>5006
pCH79ZipA(23–328)10011+
pCH172D-ZipA(23–328)5006+
  • a Overnight cultures ofzipA+ strain PB103, containing the indicated plasmids, were diluted 100-fold in fresh LB medium containing ampicillin and 0, 5, 10, 25, 50, 100, 250, or 500 μM IPTG. The cultures were incubated at 37°C to an OD600 of 0.6 to 0.8. The cells were examined by phase-contrast microscopy to determine the concentrations of IPTG at which expression of ZipA (or derivative) caused the formation of nonseptate filaments. In parallel, a portion of each culture was used to prepare a whole-cell lysate, and relative protein levels were determined by quantitative immunoblotting as described in Materials and Methods.

  • b Minimum IPTG concentration at which a clear division block was observed.

  • c Level of the plasmid-encoded ZipA protein (or derivative) in cells that were grown at this minimum IPTG concentration. For ZipA(1–302)-H, the level in cells grown with 500 μM inducer is given. Levels are expressed as multiples of the level of chromosomally encoded native ZipA in PB103/pMLB1113ΔH control cells that had been grown in the presence of 500 μM IPTG.

  • d Division phenotype at the indicated concentration of IPTG; +, division block (i.e., the majority of the cells were nonseptate filaments over 20 μm in length); −, no division block at any of the IPTG concentrations tested.

  • e Plasmid is a lacZ derivative of vector pMLB1113.