Sensing environmental changes and responding to them is the key to any organism’s survival. The simplest example of a sensor-response system is seen in bacteria in the form of what is known as the two-component system. This system involves proteins in which the sensor or component I detects the stimulus via its input or sensor domain and is trans-autophosphorylated on a conserved histidine. The sensor then transfers this phosphate to the response regulator, or component II, on a conserved aspartic acid residue (Hoch 2000).This His-Asp signal transduction pathway, though ubiquitous in prokaryotes, is rarely encountered in higher eukaryotes.