Nucleotide sequence and transcriptional regulation of a positive regulatory gene of Shigella dysenteriae.

A 1,937 bp PstI-HindIII fragment containing the ipaR locus was cloned from the large invasion plasmid of Shigella dysenteriae CG097, and its nucleotide sequence was completely determined. The IpaR protein (35 kDa, calculated from the DNA sequence) was synthesized in Escherichia coli chi 1411 minicells containing the 1,937-bp PstI-HindIII fragment. To determine the regulatory role of ipaR for ipa genes, we applied genetic complementation experiments using chloramphenicol acetyltransferase (CAT) as reporter. Analyses of CAT activity of the recombinant plasmids containing the 5' flanking sequences of the 24-kDa-protein gene and the ippI, ipaB, ipaC, and ipaD genes defined strong promoters upstream of the 24-kDa-protein gene and ipaD gene, weak promoters upstream of the ippI and ipaB genes, and the absence of any promoter activity for the ipaC gene. Complementation analyses showed that the CAT activity only under direction of the ippI promoter region increased 1.8-fold in the presence of IpaR protein. On the basis of our data, we suggest that an operon comprising ippI, ipaB, and ipaC is positively regulated by IpaR protein which has a trans effect on a DNA sequence upstream of the ippI promoter.