THE SHIGELLA VIRULENCE GENE REGULATORY CASCADE - A PARADIGM OF BACTERIAL GENE-CONTROL MECHANISMS

Shigella flexneri is the causative agent of bacillary dysentery and is a facultative intracellular pathogen. Its virulence regulon is subjec t to tight control by several mechanisms involving the products of ove r 20 genes and an array of environmental signals. The regulon is carri ed on a plasmid that is prone to instability and to integration into t he chromosome, with associated silencing of the virulence genes. Close ly related regulons are found in other species of Shigella and in ente roinvasive Escherichia coli. A wealth of detailed information is now a vailable on the Shigella virulence gene control circuits, and it is be coming clear that these shave many features with regulatory systems fo und in other bacterial pathogens. All of this makes the S. flexneri vi rulence gene control system a very attractive topic for those interest ed in the nature of gene regulatory networks in bacteria.