FIG. 6.

Secretion of full-length mutant HasA proteins with pentapeptide insertions. (A) Cells of LMD439 (att λ::hasDE) expressing a pAM-encoded wild-type (WT) or mutant form of HasA were induced for type 1 secretion with 0.02% arabinose until the late exponential phase. Following centrifugation of culture aliquots, proteins in the supernatants were precipitated with trichloroacetic acid, separated by SDS-PAGE, and visualized by Coomassie blue staining. The molecular masses of the markers (kilodaltons) are indicated at the left. (B) The levels of secretion were quantified by densitometry analysis. The results generated are based on three independent experiments and are expressed in percentages of the wild-type HasA level of secretion (100%). The dashed line indicates the arbitrary threshold of 50% reduction of secretion. Note that in the absence of arabinose, the expression levels of HasA and the mutant proteins retained in the cytoplasm are comparable (data not shown).