Two new members of the OmpR superfamily detected by homology to a sensor-binding core domain

The OmpR superfamily includes proteins that act as transcriptional regulators of operons that respond to environmental stimuli. A homologous domain near the N-terminus, termed a sensor-binding core domain, is thought to play a role in recognition of a signal transduction protein. We have identified two previously unrecognized members of this regulator family of proteins: a 23.8-kd protein transcribed from the uvrC transcription unit and the PgtA gene product, which is a phosphoglycerate transport regulatory protein. The sensor-binding core domain is also present in four proteins that regulate bacterial sporulation and chemotaxis. The 23.8-kd protein also has sequence similarity to elongation factor Tu and two regulatory proteins: HtpR, the heat-shock regulatory protein, and TraJ, a regulator of expression of genes involved in conjugation. There is a 77-amino acid region near the C-terminus of the 23.8-kd protein that has 30% similarity with a 28.1-kd protein coded for by an open reading frame 5′ to the reading frame of the 23.8-kd protein in the uvrC transcription unit. Genetic distance analysis of amino acid sequences of proteins with a sensor-binding core domain suggests that the 23.8-kd protein and the chemotaxis regulatory proteins are distantly related to the other regulatory proteins in the OmpR superfamily.