The expression of the temperature-inducible plasmid-coded outer membrane proteins (YOPs) of Yersinia pseudotuberculosis was studied. These proteins were not recovered in the outer membrane fraction when the strain was grown in minimal medium at 37 degrees C, but they were expressed under these conditions. A strict correlation was found between Ca2+ dependency in the virulent strain, YPIII(pIB1), and ability to express YOPs. Ca2+-independent plasmid mutants or RNA-polymerase mutants harboring the virulence plasmid were unable to express YOPs, in contrast to the wild-type strain. These strains were also found to be avirulent. Sera recovered from patients or animals undergoing infection with either Y. pseudotuberculosis, Y. pestis, or Y. enterocolitica possessed antibodies directed against YOPs, indicating that they were expressed in all three pathogenic Yersinia species during infection. The YOPs of the three different species showed high immunological relatedness.

Bölin, I., Portnoy, D. A., & Wolf-Watz, H. (1985). Expression of the temperature-inducible outer membrane proteins of yersiniae. Infection and Immunity, 48(1), 234–240.