Ca²⁺/calmodulin-dependent protein kinases from the neuronal nuclear matrix and post-synaptic density are structurally related

A major Ca²⁺/calmodulin-dependent protein kinase has been isolated in association with the neuronal nuclear matrix. Nuclear matrix preparations contain highly phosphorylated polypeptides with M(r) values of 50,000 and 60,000. These polypeptides were further characterized by peptide and phospho peptide mapping, two-dimensional isoelectrofocusing/NaDodSO₄/PAGE, and ¹²⁵I-labeled calmodulin binding. The results indicate that the M(r) 50,000 and 60,000 polypeptides of the nuclear matrix closely resemble the α and β subunits, respectively, of the Ca²⁺/calmodulin-dependent protein kinase of the post-synaptic density. These findings indicate that similar protein kinases mediate the neuronal effects of Ca²⁺ at the cytosolic, synaptosomal, and nuclear levels.