Expression of four virulence antigens of Shigella flexneri is positively regulated at the transcriptional level by the 30 kiloDalton virF protein.

On the virulence plasmid of Shigella flexneri the virG region required for cell-to-cell spread of the bacterium encodes a 130 kiloDalton (kD) antigen and Region-2 essential for the bacterial invasion of epithelial cells encodes 57, 43 and 39 kD antigens. The expression of these four antigens is positively regulated by the 30 kD protein encoded by virF, whose nucleotide sequence had been determined and which was previously found to be essential for virulence. An approximately 3.8 kilobase (kb) RNA transcript is found to be transcribed by the virG region and is positively regulated by the virF protein resulting in increased production of the 130 kD antigen. The virF sequence is conserved among all shigellae and enteroinvasive Escherichia coli.