CLONING AND CHARACTERIZATION OF APLYCALCIN AND APLYSIA NEUROCALCIN, 2NEW MEMBERS OF THE CALMODULIN SUPERFAMILY OF SMALL CALCIUM-BINDING PROTEINS

We report here the sequences of two new proteins from Aplysia, aplycal cin and Aplysia neurocalcin. These proteins belong to a family of calc ium-binding proteins, found primarily in vertebrate brain and retina, that have been proposed to play a role in calcium-dependent regulation of enzymes in signal transduction pathways. Like other members of thi s family, the Aplysia proteins have consensus sequences for myristoyla tion, bind calcium, and translocate from cytosol to membrane when the calcium level is raised above the resting intracellular concentration. Both proteins are relatively enriched in Aplysia nervous system, but are also found to a significant degree in other tissues, The expressio n of mRNA for these proteins in Aplysia nervous tissue is regulated du ring development, roughly paralleling the reported emergence of severa l forms of synaptic plasticity, The messages are present at low levels in stage 11, show a large increase by late stage 12, and decline to a plateau of similar to 30% of the peak value afterward, On the basis o f the properties of these proteins and by analogy with proposed functi ons of some of the retinal homologues, we suggest that these proteins may play a role in mediating calcium-dependent processes in neuronal f unction, The presence of both proteins in other tissues may suggest an alogous roles for the proteins in other cell types.