Perinuclear Membrane Localization of αKAP, a Protein Produced from a Gene within the Gene of Calmodulin-Dependent Protein Kinase IIα

Abstract

αKAP is a protein produced from a gene within the gene of the α isoform of calmodulin-dependent protein kinase II (CaM-kinase IIα). It consists of the association domain of CaM-kinase IIα and a highly hydrophobic amino-terminal stretch consisting of 25 amino acids which is absent from CaM-kinase IIα. We previously demonstrated that αKAP is an integral membrane protein by subcellular fractionation analysis [Sugai, R., Takeuchi, M., Okuno, S., and Fujisawa, H. (1996) J. Biochem. 120, 773-779], but the exact subcellular localization of αKAP was not well understood. Here we demonstrate that αKAP is localized on the nuclear membrane of COS-7 cells transiently expressing αKAP. The nuclear membrane and perinuclear small vesicles were immunostained with an antibody against a synthetic peptide corresponding to the carboxyl-terminal 15 amino acids of αKAP. In contrast to the intact αKAP, the mutant αKAP, from which the hydrophobic aminoterminal segment had been deleted, accumulated within nuclei. Thus, αKAP may function as an anchoring protein for CaM-kinase II and/or other proteins in the perinuclear membrane.