A Haemophilus influenzae gene encoding a protein with high homology to ArcB receptor protein from Escherichia coli has been cloned. An error in the previously reported sequence of this gene has been found, thus increasing its open reading frame. The cloned gene comprising the entire open reading frame restores oxygen-dependent regulation of succinate dehydrogenase in an ArcB-deficient E. coli strain. Thus, this gene is a functional analog of ArcB from E. coli. By screening partially sequenced bacterial genomes using the BLAST program, proteins with high homology to ArcB protein from E. coli were found in Salmonella typhi, Yersinia pestis, Vibrio cholerae, and Pasteurella multocida. Comparison of these proteins with ArcB protein from E. coli and H. influenzae revealed conserved amino acid regions. Transmembrane helix II was shown to be highly homologous in all the ArcB-type proteins. The involvement of this region in ArcB-mediated oxygen-dependent regulation is suggested.