Transcription regulator that can specifically activate or repress expression of target genes. Activates expression of genes such as molecular chaperones (groL, groS, dnaK, grpE, and cbpA), proteins involved in acid resistance (hdeA, hdeB, and gadA), the starvation lipoprotein slp, virulence protein hlyE/clyA. Represses expression of genes involved in the histidine biosynthetic pathway such as hisA, hisB, hisD, hisF and hisG. Required for the activation of virulence genes. Homodimer. Belongs to the SlyA family. Extended N-terminus. Extended N-terminus.