FIG 3.

Restoring the length of truncated substrates is not sufficient for CtpA-dependent degradation. (A) MepM immunoblot analysis of equivalent amounts of whole-cell lysates of ctpA⁺ and ΔctpA strains. Strains contained an arabinose-inducible expression plasmid encoding wild-type MepM or derivatives with 7 amino acids removed from the C terminus or with the C-terminal 7 amino acids replaced by AGEAGHL. (B) PA1199 immunoblot analysis of equivalent amounts of whole-cell lysates of ctpA⁺ and ΔctpA strains (an asterisk indicates a protein cross-reactive with the PA1199 antiserum). For PA1199 analysis, both strains also had a Δprc mutation to eliminate any interference from degradation of mutant proteins by Prc. Strains contained an arabinose-inducible expression plasmid encoding wild-type PA1199 or derivatives with 7 amino acids removed from the C terminus or with the C-terminal 7 amino acids replaced by AGEAGHL. For both panels, strains were grown in medium containing arabinose. MepM and PA1199 were detected with polyclonal antisera, and a Ponceau S total protein stain of the same region of the nitrocellulose membrane is shown to document loading levels. Immunoblots are single representatives of several replicate experiments.