This family consists of a number of bacterial sequences which are highly similar to the Tir chaperone protein in E. Coli. In many Gram-negative bacteria, a key indicator of pathogenic potential is the possession of a specialized type III secretion system, which is utilized to deliver virulence effector proteins directly into the host cell cytosol. Many of the proteins secreted from such systems require small cytosolic chaperones to maintain the secreted substrates in a secretion-competent state. CesT serves a chaperone function for the enteropathogenic Escherichia coli (EPEC) translocated intimin receptor (Tir) protein, which confers upon EPEC the ability to alter host cell morphology following intimate bacterial attachment. This family also contains several DspF and related sequences from several plant pathogenic bacteria. The "disease-specific" (dsp) region next to the hrp gene cluster of Erwinia amylovora is required for pathogenicity but not for elicitation of the hypersensitive reaction. DspF and AvrF are small (16 kDa and 14 kDa) and acidic with predicted amphipathic alpha helices in their C termini; they resemble chaperones for virulence factors secreted by type III secretion systems of animal pathogens.