Posttranslational modification of protein kinase A. The link between short-term and long-term memory

Both for Aplysia and Drosophila a key role in the molecular mechanism of learning and memory processes has been assigned to the cAMP cascade. In any learning process a short-time stimulus has to be translated into long-lasting changes. The molecular correlate must be a cascade of biochemical reactions with different kinetics, functionally interlinked and operating in overlapping time ranges. Biochemical studies in Drosophila have led to the suggestion that one of these steps is a proteolytic modification of the regulatory subunits of protein kinase A. A quantitative analysis of the relaxation kinetics of a system of protein kinase A, phosphatases and a calcium-dependent protease can give an image of essential characteristics of learning behaviour in Drosophila.