Temperature regulation of Shigella virulence: identification of the repressor gene virR, an analogue of hns, and partial complementation by tyrosyl transfer RNA (tRNA1Tyr)

Abstract

virR is the central regulatory locus required for coordinate temperature-regulated virulence gene expression in the human enteric pathogens of Shigella species. Detailed characterization of VirR⁺ clones revealed that virR consisted of a 411 bp open reading frame (ORF) that mapped to a chromosomally located 1.8kb EcoRI-Accl DNA fragment from Shigella flexneri. Insertional inactivation of the virR ORF at a unique Hpal restriction site resulted in a loss of VirR⁺ activity. The vir R ORF nucleotide sequence was virtually identical to the Escherichia coli hns gene, which encodes the histone-like protein, H-NS. Based on the predicted amino acid sequence of E. coli H-NS, only a single conservative base-pair change was identified in the virR gene. An additional clone, designated VirR^P, which only partially complemented the virR mutation, was also characterized and determined by Southern hybridization and nucleotide sequence analysis to be unique from virR. Subclone mapping of this clone indicated that the VirR^P phenotype was a result of the multiple copy expression of the S. flexneri gene for tRNA^Tyr. These data constitute the first direct genetic evidence that virR is an analogue of the E. coli hns gene, and suggest a model for temperature regulation of Shigella species virulence via the bacterial translational machinery.