ABSTRACT
Evolutionarily advanced species such as myxobacteria use the stringent response for a more sophisticated survival strategy: the formation of multicellular spore capsules. Ion channels are absolutely essential for metabolism, equalization of osmotic pressure, and regulation of intracellular acidity. In parallel they were employed for data processing from the very beginning of life. The separation of sensor protein and His kinase is highly economical since it allows a single signal-processing apparatus to be stimulated by a wide variety of environmental signals, thus enabling an integrated response of the cell. Apart from the lack of intrinsic His kinase activity, the sensors of tactic signals resemble conventional sensor His kinases in that they exist as dimers with mostly two pairs of transmembrane helices with a variable signal recognition site at the outside and a conserved cytoplasmic domain. These chemoreceptors are known as methyl-accepting chemotaxis proteins since they become methylated at several carboxyl groups in the course of a chemotactic response.
