Represses EHEC virulence expression. Down-regulates expression of LEE (locus of enterocyte effacement) and iraD genes, and alters AE (attaching and effacing) lesion formation. May regulate transcription through interactions with another HTH DNA-binding protein. Transcription decreases during mid-log phase and is maximal during stationary phase. Belongs to the LysR transcriptional regulatory family. Exists in some isolates as a HTH-truncated isoform. This short isoform is still able to regulate gene expression.