Regulation and expression of Lcr plasmid-mediated peptides in pesticinogenic Yersinia pestis

It is shown in this thesis that cells of Lcr+, Pst- Y. pestis KIM are able to express Yops at levels comparable to that of Lcr+ Yersinia pseudotuberculosis. Pulse-chase radiolabeling with 35S-methionine was used to demonstrate that Lcr+, Pst+ Y. pestis synthesized at least 11 distinct peptides during the low calcium response and that seven of the labeled peptides were rapidly degraded. These seven peptides were stably expressed in Lcr+, Pst- Y. pestis and were of identical molecular weights as the Yops expressed by that strain. Radiolabeled fragments of low molecular weight accumulated in the extracellular medium of Pst+ cultures and were assumed to be stable degradation fragments derived from Yops. It was also shown that the set of stable peptides, including V antigen, were made during restriction by both Pst+ and Pst- Y. pestis KIM and were located primarily within the cytoplasm. Those radiolabeled peptides which underwent proteolytic degradation in Pst+ Y. pestis were localized to the outer membrane and extracellular medium in the Pst- strain. It is concluded that the failure of Lcr+, Pst+ Y. pestis to express Yops is the result of post-translational degradation and is not a block in the synthesis of Yops