The Salmonella YopJ-homologue AvrA does not possess YopJ-like activity

The YopJ protein of Yersinia pseudotuberculosis inhibits several eukaryotic signalling pathways that are normally activated in cells following their c ontact with bacteria. Salmonella encodes a protein, AvrA, that is secreted by the typeIII inv/spa secretion system which is clearly homologous to YopJ (56% identical, 87% similarity). Since AvrA and YopJs similarity also enco mpassed a region of YopJ that had previously been shown to be critical for its biological activity, we were interested whether AvrA and YopJ provoked similar responses in eukaryotic cells. Two different approaches were used t o determine whether AvrA possesses YopJ-like activity in modulating cytokin e expression or killing macrophages. An avrA strain of Salmonella dublin wa s constructed and its activity was compared to an isogenic wildtype counter part in cellular response assays. In a complementary approach, AvrA was exp ressed in and delivered into eukaryotic cells by a yopJ strain of Yersinia pseudotuberculosis. We show here that AvrA affects neither cytokine express ion or plays a role in macrophage killing when expressed by either Salmonel la or Yersinia. Additionally, AvrA does not possess SopB/D-like activity in promoting fluid secretion into infected calf ileal loops. These data indic ate that Salmonella and Yersinia trigger and/or modulate eukaryotic cell re sponses by different typeIII-secreted proteins and suggests that despite th eir close evolutionary relatedness, AvrA and YopJ perform different functio ns for Salmonella and Yersinia, respectively. (C) 2000 Academic Press.