The FimZ protein, an activator of FimA production in Salmonella typhimurium, acts in conjunction with FimY to facilitate the expression of type 1 fimbriae. The predicted amino acid sequence of FimZ suggests that this protein may be a DNA-binding protein related to BvgA, a sensory regulator of virulence gene expression in Bordetella pertussis. Purification of FimZ following overexpression of the protein by a strong inducible promoter and gel mobility shift assays confirm that FimZ is a 25-kDa polypeptide that binds to the promoter region offimA. The region of DNA protected from DNase I digestion by FimZ binding is located between 47 and 98 nucleotides upstream from thefimA transcription initiation site. This region possesses a pair of 7-base pair tandem repeats, of which at least one is necessary for FimZ binding. One copy of the 7-base pair sequence is also located in thefimZ promoter region. In addition, expression from afimZ-lacZ reporter construct confirms that FimZ plays a role in its own expression. Both FimZ and FimY are required for high-level expression of FimZ, which suggests that these two fimbrial proteins are involved in regulating both FimA and FimZ.