CELLULAR INTERNALIZATION IN THE ABSENCE OF INVASIN EXPRESSION IS PROMOTED BY THE YERSINIA-PSEUDOTUBERCULOSIS-YADA PRODUCT

The Yersinia pseudotuberculosis invasin protein is able to promote bac terial penetration into mammalian cells. Insertion mutations that elim inate production of this protein show residual internalization that is dependent on the presence of the Yersinia virulence plasmid. An enric hment procedure was used to isolate molecular clones containing region s of the virulence plasmid that confer this low-level uptake on Y. pse udotuberculosis inv mutants. All of the Y. pseudotuberculosis strains isolated from this procedure harbored plasmids containing a region enc ompassing the yadA gene, which encodes a previously identified adhesin associated with attachment to extracellular matrix proteins. All of t he mutations isolated that affected internalization of one of the stra ins that survived the enrichment disrupted the yadA open reading frame . Furthermore, a strain that contained yadA sequences and no other reg ion of the virulence plasmid was able to promote internalization of a Y. pseudotuberculosis inv mutant. Consistent with these results, an in tact virulence plasmid containing an insertion mutation in yadA was as defective as a plasmid-cured strain at promoting uptake of Y. pseudot uberculosis inv mutants. These results indicate that the product of th e yadA gene is responsible for the plasmid-dependent entry observed in Y. pseudotuherculosis inv mutants.