FIG. 5.

yopE codons 8 to 15 contain additional secretion information. (A) Suppression of a yopE codon 3 mutation by the addition of downstream codons was measured by introducing the U8A transversion into successively longer yopE secretion signals and fusion to npt. (B) The minimum number of yopE codons required to tolerate a frameshift mutation. One nucleotide immediately following the AUG start codon was deleted to introduce a −1 frameshift in the yopE reading frame. The reading frame was restored by addition of an adenyl immediately after the 3′ end of the yopE sequence before fusion to npt. Fusions to Npt were analyzed for type III secretion as described in the legend to Fig. 1.