THE COATOMER PROTEIN BETA'-COP, A SELECTIVE BINDING-PROTEIN (RACK) FOR PROTEIN-KINASE C-EPSILON

Distinct subcellular localization of activated protein kinase C (PKC) isozymes is mediated by their binding to isozyme-specific RACKs (recep tors for activated C-kinase), Our laboratory has previously isolated o ne such protein, RACK1, and demonstrated that this protein displays sp ecificity for PKC beta. We have recently shown that at least part of t he PKC epsilon RACK-binding site on PKC epsilon lies within the unique V1 region of this isozyme (Johnson, J. A., Gray, M. O., Chen, C.-H., and Mochly-Rosen, D. (1996) J. Biol, Chem. 271, 24962-24966), Here, we have used the PKC epsilon V1 region to clone a PKC epsilon-selective RACK, which was identified as the COPI coatomer protein, beta'-COP. Si milar to RACK1, beta'-COP contains seven repeats of the WD40 motif and fulfills the criteria previously established for RACKs. Activated PKC epsilon colocalizes with beta'-COP in cardiac myocytes and binds to G olgi membranes in a beta'-COP-dependent manner, A role for PKC in cont rol of secretion has been previously suggested, but this is the first report of direct protein/protein interaction of PKC epsilon with a pro tein involved in vesicular trafficking.