INTRODUCTION. Several animaland plant-interacting Gram-negative bacteria possess the socalled type III secretion system or TTSS, which functions to inject proteins (or ‘effectors’) directly into eukaryotic cells[1]. TTSS effectors play important roles in a variety of host-microbe interactions including Rhizobium-mediated root nodulation, plant hypersensitivity reactions, and in animals, modulating immune responses. The pathogenic yersiniae (Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica) inject five TTSS effectors all of which are required for full virulence in the mouse model. As might be expected since they function within host cells, Yersinia’s TTSS effectors possess clear eukaryotic-like protein domains or motifs. One of these effectors, the Yersinia protein kinase A (YpkA), contains the canonical 11 subdomains (I-XI) characteristic of eukaryotic ser/thr protein kinases with a highly conserved catalytic core sequence. In addition to the amino-terminally located kinase domain, YpkA, also contains in its carboxyl-terminal region sequences that resemble eukaryotic RhoA-binding domains.