Reverse transcription polymerase chain reaction data indicate that yitA, -B, -C genes form an operon and yipA, -B genes are on a different transcriptional
unit . Deletion of the upstream LysR-like regulator (yitR) decreased the production of Tc proteins , indicating that YitR, which is also upregulated following growth of Y. pestis in the flea , is a positive regulator of expression. Similarly to P. luminescens, Y. pestis Tc proteins form a large multicomponent protein FRAX597 mouse complex that contains all 5 Tc proteins . Complex formation requires YitA and YitB, and YitC is necessary for association of YipA and YipB with the complex . Figure 1 A) The Tc protein locus of Y. pestis contains the yitABC and yipAB insecticidal-like protein genes and the upstream regulator yitR . Alignment of the Tc locus for all sequenced Y. pestis strains is shown with differences from KIM10+ JSH-23 cost indicated. The deletions in the Y. pestis KIM6+ΔyitR and ΔyitA-yipB mutant strains used in this study are indicated. B) Domain
structure of YitA and YipA. Hatch marks represent the region of YitA with similarity to the Salmonella virulence plasmid A (VRP1) protein family. The light gray area designates the region of YipA similar to the Rhs protein family. Light gray shaded hatch marks indicate the RHS repeat-associated core domain. Dark gray represents the region sharing homology to the protein tyrosine phosphatase (PTP) protein family and the PTP catalytic NCT-501 order domain. The arrow next indicates the inferred location of post-translational processing of YipA. The translational fusion junction of the full-length YitA and YipA with the mature β-lactamase is designated by shaded triangles. Although there is no defined biological role for the Yersinia Tc proteins, functional
studies indicate that they are important in the interaction with insect cells or specific mammalian host cells. Y. pestis Tc proteins are not toxic to M. sexta, whereas Y. pseudotuberculosis and Y. enterocolitica (biotype 2–5, including strain W22703) Tc proteins are toxic, although they are much less potent than P. luminescens toxins [12, 21, 22]. Whereas P. luminescens toxins are also toxic to Xenopsylla cheopis rat fleas, Y. pestis and Y. pseudotuberculosis Tc proteins are not . Additionally, Y. pseudotuberculosis and Y. pestis Tc proteins are not active against Spodoptera frugiperda (Sf9) insect cells . However, unlike Y. pseudotuberculosis, Y. pestis Tc proteins are active against NIH 3T3 mouse fibroblast cells but not Caco-2 human intestinal epithelial cells , indicating specificity for certain host environments. There is evidence for T3SS-dependent translocation of Y. pestis Tc proteins into host cells  and Tc genes (yitA, -B, -C) are upregulated within J774A.1 macrophages .