FIG. 6.

YscI mutants exhibit defects in needle assembly. (A) Either wild-type YscI or the indicated YscI mutant forms were expressed in trans in the yscI null strain SAL4. Bacteria were grown in BHI-plus-calcium medium, and surface proteins were cross-linked via the addition of 2.5 mM BS³. Samples were run on SDS-PAGE gels, and the needle component YscF was detected by Western blotting using 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) Either wild-type YscI or the indicated YscI mutant forms were expressed in trans in the yscI null strain SAL4. Bacteria were grown in BHI-minus-calcium medium, and YscF was cross-linked and detected as described above.