Fig. 1. Fewer and shorter P pili are assembled without the Cpx signaling pathway. (A) P pili were purified by Galα(1–4)Gal affinity chromatography in lanes 1–4 and by MgCl₂ precipitation in lanes 5–8, run on SDS–PAGE and stained with Coomassie Blue. Pili were purified after 3 days passage on TSA plates from the following strains: wild-type strain alone, lanes 3 and 7 (MC4100); wild-type strain expressing P pili, lanes 1 and 5 (MC4100/pPAP5); cpxR null strain alone, lanes 4 and 8 (TR51); and cpxR null strain expressing P pili, lanes 2 and 6 (TR51/pPAP5). The arrow points to the PapA band. (B) Negative stain of wild-type cells expressing P pili (MC4100/pPAP5) at a magnification of 20 000. (C) Negative stain of cells with a cpxR null allele expressing P pili (TR51/pPAP5) at a magnification of 20 000.