During bacterial chemotaxis, motile bacteria modulate their swimming behavior in response to environmental stimuli. At the molecular level, a histidine kinase, CheA, acts as an input-output element that couples sensory information to the swimming behavior of a bacterium. This thesis focuses on the signal transmission in the domains of CheA, including identification of the interaction site between CheA's regulatory domain and the cytoplasmic domain of chemoreceptor, establishment of the roles of two interdomain linkers in the signal transduction pathway, and the elucidation of how the interdomain linker that connects the dimerization and ATP-binding domains assumes its functional role. These findings extend our understanding of the chemotaxis signal transduction pathway.