HmsT, a protein essential for expression of the haemin storage (Hms+) phenotype of Yersinia pestis

The haemin storage (Hms) phenotype of Yersinia pestis has been shown to be involved in the blockage of fleas that is required for the transmission of plague from fleas to mammals. Previously, an operon encoding four genes, hmsHFRS, that are essential for the temperature-regulated Hms+ phenotype has been characterized. Here the isolation and characterization of a fifth gene, hmsT, that is essential for this phenotype is described. Conceptual translation of hmsT suggests it encodes a 44.8 kDa protein with a pl of 7.75. The gene for HmsT is located outside of the approximately 102 kb pgm locus of Y. pestis that contains the hmsHFRS operon. Hybridization studies indicate that Yersinia pseudotuberculosis but not Yersinia enterocolitica or Escherichia coli possesses a highly homologous gene. HmsT belongs to a family of PleD-related proteins with four highly conserved regions of homology. Although PleD is a regulator, the functions of the other members of this family have not been experimentally determined. The iron-responsive regulator, Fur, has previously been implicated in temperature regulation of the Hms phenotype. A good potential Fur-binding site (FBS) is located upstream of hmsT. Y. pestis M23 and two of five Y. pseudotuberculosis strains, which all exhibit a temperature-constitutive Hms phenotype, contain a 6 bp insertion in the putative FBS. E. coli MG1655 contains homologues of hmsHFRST (ycdSRQPT) but has an Hms- phenotype. Only ycdQ and ycdP complement mutations in their respective homologues, hmsR and hmsS, in Y. pestis.