Draft Prokaryotic two - component systems and the OmpR / PhoB superfamily

23 In bacteria, two-component regulatory systems (TCSs) are the critical information-processing 24 pathways that link stimuli to specific adaptive responses. Signals perceived by membrane 25 sensors, which are generally histidine kinases (HKs), are transmitted by response regulators 26 (RRs) to allow cells to cope rapidly and effectively with environmental challenges. Over the 27 past few decades, genes encoding components of TCSs and their responsive proteins have 28 been identified, crystal structures have been described, and signaling mechanisms have been 29 elucidated. Here, we review recent findings and interesting breakthroughs in bacterial TCS 30 research. Furthermore, we discuss structural features, mechanisms of activation/regulation, 31 and cross-regulation of RRs with a focus on the largest RR family, OmpR/PhoB, to provide a 32 comprehensive overview of these critically important signaling molecules. 33