Characterization of a hemin-storage locus ofYersinia pestis

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Abstract
The pigmentation phenotype (Pgm+) ofYersinia pestis refers to temperature-dependent storage of hemin as well as expression of a number of other physiological characteristics. Spontaneous mutation to a Pgm− phenotype occurs via a large chromosomal deletion event and results in the inability to express the Pgm+ characteristics. In this study, we have used transposon insertion mutants to define two regions of a hemin-storage (hms) locus. A clone (pHMSI) encompassing this locus reinstates expression of hemin storage (Hms+) inY. pestis spontaneous Pgm− strains KIM and Kuma but not inEscherichia coli. Complementation analysis using subclones of pHMS1 inY. pestis transposon mutants indicates that both regions (hmsA andhmsB), which are separated by about 4 kb of intervening DNA, are essential for expression of the Hms+ phenotype. The 9.1-kb insert of pHMS1 contains structural genes encoding 90-kDa, 72-kDa, and 37-kDa polypeptides. Two-dimensional gel electrophoresis analysis of cells from Pgm+, spontaneous Pgm−, and Hms− transposon strains, as well as a spontaneous Pgm− strain transformed with pHMS1, indicated that two families of surface-exposed polypeptides (of about 87 and 69-73 kDa) are associated with the Hms+ phenotype.