Identification of a Shigella flexneri criR gene increasing ipa genes expression: a novel member of response regulators of the two-component signal transduction family.

A genetic locus named cri, which enhanced the expression of ipa genes, was cloned into Escherichia coli K-12 from Shigella flexneri 1b chromosomal DNA. Subcloning and Tn5-Tc1 transposon experiments showed that cri locus was located on a 2.6-kb HindIII fragment. Nucleotide sequence analysis of the region revealed at least three open reading frames (ORF), one of which, named criR, encoded a protein of 226 amino-acid residues and transcriptionally increased the ipaB expression. The deduced regulatory protein CriR shared a significant homology with bacterial transcriptional activators of the two-component signal transduction family. A homologue of the criR gene was present in genomic DNA of Shigella spp. and E. coli strains, and mapped at the 14.6-min region of E. coli K-12 chromosomal DNA. These results indicate that criR is a new member of response regulators.