Functional analysis of the VirB protein of Shigella flexneri

Abstract

The VirB protein is a key regulator of virulence gene expression in Shigella flexneri, a facultative enteroinvasive pathogen that causes bacillary dysentery. Genetic evidence has shown that VirB is required for the activation of transcription of virulence genes located on the 230 kb large virulence plasmid and it has been generally assumed that the protein acts as a conventional transcriptional activator. However, hitherto no evidence has been presented in support of this assumption. Interestingly VirB does not resemble any known conventional transcription factor but shares extensive homology with a family of proteins involved in plasmid partitioning.