FIG. 4.

Mutations in yscU reduce YscI export by a yscP mutant. Mutations in the cytoplasmic domain of YscU were introduced in trans into the yscP yscU double null strain SAL3. Bacteria were grown at 37°C in BHI-plus-calcium medium, and YscU expression was induced with 0.2% arabinose. Secreted supernatant (SN) and cell pellet (P) fractions were separated by centrifugation, and proteins in the supernatant were TCA precipitated. Equal percentages of secreted supernatant and cell pellet fractions were run on SDS-PAGE gels. YscI was detected by Western blotting with a polyclonal antiserum (upper panel); the cytoplasmic protein GroEL was detected with a monoclonal antibody (lower panel). pBAD18, vector control; pYscU-WT, plasmid expressing wild-type YscU; pYscU-Y287G, plasmid expressing YscU with the Y287G mutation; pYscU-Y317D, plasmid expressing YscU with the Y317D mutation.