Fig 4. The co-translational DsbA signal sequence, but not the post-translational PhoA signal sequence, bypasses lethality.

(A) Production and secretion of pertactin chimera constructs in the E. coli degP null strain versus its parent. Bacteria were grown to stationary phase and protein production was analyzed by western blotting of whole cell lysates. Successful secretion of the pertactin passenger is measured by appearance of the processed passenger [24,25,29,32,50]. Two non-adjacent portions of the same blot are shown (grey line). (B) Expression of signal sequence chimera constructs does not dramatically affect growth of wild type E. coli. (C) Plasmids to express dsbA(ss):prn and phoA(ss):prn under control of a constitutive promoter were transformed in the E. coli degP null mutant versus its parent as described in Fig 2A. Error bars are standard deviations from at least three biological replicates. (D) Expression of dsbA(ss):prn, dsbA(ss):prnΔβ-barrel and pet does not affect growth in the degP null strain. (B, D) Shown are representative growth curves.