FIG 3.

(A) Membrane topology model of ColM-type immunity proteins in pseudomonads. PmiA carries 4 predicted TMHs, the first of which may act as a Sec- or Tat-dependent signal sequence (rectangle). The putative ColM immunity partner PmiB (in shaded box) has a periplasmic domain and is anchored in the inner membrane (IM), but PmiB-encoding genes are absent from P. aeruginosa genomes. PmiC has 6 TMHs and occurs exclusively in P. aeruginosa. N indicates the amino terminus. Pseudomonas ColM-type immunity proteins were drawn as in reference 27. (B) SDS-PAGE gel of purified recombinant PaeM4. Lane 1, Kaleidoscope ladder, with sizes indicated in kilodaltons; lane 2, purified His-tagged PaeM4 (∼41 kDa; predicted size, 39.99 kDa). (C and D) Spot assay of 10-fold serial dilutions of PaeM4 (initial concentration, 1 mg/ml) against P. aeruginosa Br993 on CAA medium, in the absence (C) or presence (D) of 50 μM FeCl₃.