Summary auto-generated
This study identifies and characterizes hmsT, a fifth gene essential for the haemin storage (Hms) phenotype in Yersinia pestis. The Hms phenotype enables blockage of flea foreguts, which is critical for plague transmission from fleas to mammals. Previously, four genes (hmsHFRS) located within a 102 kb pgm locus were identified as required for temperature-regulated Hms expression. Through mini-kan mutagenesis and genetic complementation, the authors isolated hmsT, located outside the pgm locus. The hmsT gene encodes a predicted 44.8 kDa protein belonging to a PleD-related family of proteins with four conserved homology regions. A putative Fur-binding site upstream of hmsT suggests iron-responsive regulation. Notably, strains carrying mutations in the Fur-binding site show constitutive Hms expression regardless of temperature. The hmsT gene is present in Y. pseudotuberculosis but absent from Y. enterocolitica and E. coli. When all five hms genes (hmsHFRST) were provided to E. coli or Y. enterocolitica, both strains showed constitutive Hms expression, indicating these five genes are jointly required for the phenotype.
Key findings
- HmsT is a 44.8 kDa protein essential for temperature-regulated haemin storage phenotype in Y. pestis, located outside the pgm locus that contains hmsHFRS
- The hmsT gene contains a putative Fur-binding site and belongs to a PleD-related protein family with four conserved homology regions
- Only Y. pseudotuberculosis possesses a homologous hmsT gene among tested Yersinia species and E. coli
- All five hms genes (hmsHFRST) are required together for proper Hms phenotype expression in Y. pestis, Y. enterocolitica, and E. coli
- Multiple copies of hms genes cause loss of temperature regulation, suggesting gene dosage affects the regulatory mechanism
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Abstract
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 pI of 7.75. The gene for HmsT is located outside of the approx. 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.