FIG. 7.

YscF secretion by YscI mutants. (A) Either wild-type (WT) YscI or the indicated YscI mutants were expressed in trans in the yscI null strain SAL4. Bacteria were grown in Yop-inducing medium (BHI minus calcium), and YscI expression was induced with 20 μM IPTG. Secreted supernatant and cell pellet fractions were separated by centrifugation. Secreted proteins were precipitated with TCA, and equal percentages of the two fractions were run on SDS-PAGE gel. YscF was detected by Western blotting with a polyclonal antiserum. pSE380, vector control; pYscI-WT, plasmid expressing wild-type YscI; pYscI-Q84A to pYscI-L111A, plasmids expressing YscI proteins with the indicated mutations. (B) The same fractions described above were probed with a monoclonal antibody against the cytoplasmic protein GroEL.