Several steps in the stimulus response coupling mediated by Ca2+ and calmodulin were investigated: (1) The existence of a GTP- specific diacylglycerol kinase which phsophorylates a specific pool of diacylglycerol has been demonstrated. This novel GTP- regulated protein may play a role in the release of Ca2+ from internal stores upon external stimuli. (2) Ca2+ binding by calmodulin is subject to a regulation by Mg2+ which appears to be mediated by a Mg2+-induced conformational change in the central helix connecting the two halves of the calmodulin molecule. (3) The catalytic subunit of calcineurin, a calmodulin-regulated protein phosphatase, contains four distinct function domains. The calmodulin-binding domain of calcineurin has been isolated and characterized. Genes for the two subunits of calcineurin have been cloned and their sequence is being determined. The availability of the amino acid sequence of the two proteins will permit mapping of the functional domains of the enzyme and further our understanding of the mechanism of activation by calmodulin. (4) In collaboration with Drs. Tash and Platter we have obtained evidence for a role of calcineurin in the regulation of cell motility and exocytosis. Stimulus response coupling by cAMP being studied by J. Foster who has cloned, sequenced and mapped the gene for the catalytic subunit of cAMP-dependent protein kinase of Drosophila melanogaster. The gene encoding the cGMP-dependent kinase of the same organism has also been isolated and is being sequenced.
