FIG. 4.
Mutations within the minimal secretion signal of yopN. To identify nucleotide positions that are important for the function of the secretion signal of yopN, nucleotide transversions (purine and/or pyrimidine substitutions) were introduced into yopN1-12. The variant signals were fused to npt, yopN1-12-npt was cloned on low-copy-number vectors, and recombinant plasmids were then transformed into Y. enterocolitica strain W22703. In the event that a stop codon would have been introduced by the transversion (codon 9), an alternate nucleotide was used for mutagenesis. Bacteria were induced for type III secretion, cultures were fractionated, and YopN-Npt secretion was measured as described in the legend to Fig. 1.