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Cell signalling has arguably become one of the most important aspects of modern biochemistry and cell biology (Gomperts, 2004; Hancock, 2005). The ability of organisms to perceive and correctly respond to their microenvironment is crucial to their survival. The perception of signals such as osmotic strength, pH, oxygen, light, the availability of food, and the presence of predators or competitors for food is fundamental to life. These signals provoke appropriate responses, such as motion away from toxic substances or toward food. In multicellular organisms, cells with various functions process an extensive variety of signals ranging from variations in sunlight to the presence of growth hormones. For animal cells, the interdependent metabolic activities in various tissues or the concentrations of glucose in extracellular fluids, for example, present vital signals that have to be handled. These signals convey information that is detected by receptors and converted to a cellular response. In this context, signal transduction can be defined as the conversion of information into chemical change-a universal property of living cells (Nelson and Cox, 2008). A relatively small stimulus commonly provokes an avalanche of responses: in typical signal transduction processes the number of participating proteins increases tremendously as the process emanates from the initial stimulus, resulting in a ‘signal cascade’(Hunter, 2000; Pawson and Nash, 2003). In many cases, the result of a signalling pathway is the posttranslational modification of target-cell proteins that change their activities. Almost all of the more than 200 kinds of posttranslational modifications that occur …