DNA sequence and product analysis of the virF locus responsible for congo red binding and cell invasion in Shigella...

The DNA sequence of virF, a locus associated with virulence and the ability to bind Congo red in Shigella flexneri 2a that is located on a 140-megadalton (230-kilobase) plasmid, was determined and analyzed. It was rich in A and T. The direction of transcription of virF was determined by using a chloramphenicol resistance cartridge. An open reading frame readable in this direction was found. Three proteins, 30, 27, and 21 kilodaltons, all corresponding to those predicted from the above sequence, were produced in minicells containing the virF locus. The three proteins were expressed only weakly in minicells with the 230-kilobase plasmid.