PHOSPHORYLATION OF THE CONDITIONING-ASSOCIATED GTP-BINDING PROTEIN CP20 BY PROTEIN-KINASE-C

The phosphorylation state of cp20, a low molecular weight membrane-ass ociated GTP-binding protein, was previously shown to increase two- to threefold 24 h after associative conditioning. Here, cp20 is shown to be phosphorylated by protein kinase C (PKC) in vitro. Pronounced diffe rences in activity were observed with the three major isoforms of PKC, whereas casein kinase, calcium/calmodulin-dependent protein kinase II , and cyclic AMP-dependent protein kinase produced no detectable phosp horylation of cp20. Phosphorylation of cp20 had no effect on its GTPas e or GTP-binding activity but caused a translocation of cp20 from cyto sol to the nuclei/mitochondrial particulate fraction. These results su ggest that the increase in phosphorylation of cp20 after conditioning may be due to PKC.