||STUDIES ON THE SIGNAL TRANSDUCTION NETWORK OF TWO COMPONENT SYSTEMS IN ESCHERICHIA COLI
For survival, organisms adapt to environmental changes by switch the gene expression. Simple unicellular organisms that possess only thousands of genes such as bacteria shows the amazing adaptation ability against a variety of environment. Therefore, in bacteria, limited gene regulation mechanism may forms the transduction network with others for multiply the gene regulation pathway. Two component system which is the major signal transduction pathway employed in wide varieties of bacteria, is generally composed of the sensor kinase (SK) that monitors an external signal(s) and the response regulator (RR) that controls physiological activities for response against external signals. A total of about 30 unique TCS pairs of SK and RR have been identified in E. coli based on the gene organization and the further genetic and/or biochemical data. In addition to these, there is the several RRs which pairing partner SK are not found and its function are unkown in E.coli. The process of TCS signal transduction generally show a high level of specificity, while a certain level of cross-regulation has been identified at the signal transduction pathways in E. coli: cross talk in recognition of signals by the sensor SK (stage 1); cross talk in phosphorylation of RRs by SKs (stage 2); and cross talk in recognition of regulation target promoters between RRs (stage 3). Cross talk between TCS pairs has been established at three stages of the signal transduction pathways. Network formation between the TCSs may contribute for the bacterial adaptation to various environment. However, the perspective of the TCS network does not yet become clear. Especially, there are few reports for the cross recognition of the promoter by RRs. And E. coli possesses function unknown orphan RRs. In this study, for the elucidation of the entire signal transduction network of E. coli, I performed the comprehensive analysis of the stage 3 cross talk among RRs. And I investigated the role and activation mechanism of uncharacterized orphan RR. The study of the stage 3 cross talk between NarL-family RRs is described in the chapter 2. In the same line study, the cross talk between OmpR family RRs were also analyzed and described in chapter 3. The chapter 4 focuses on the uncharacterized RR YgeK. Taking all the chapter together, my thesis presents the specific and complicated promoter recognition by RRs and function of atypical RR YgeK that plays the role of growth in acetate medium and biofilm formation. These findings provide the insight into the perspective of TCS signal transduction network and contribute for understanding the mechanism how bacteria adapt and survive againt to environment change.