CaMKII, calcium/calmodulin dependent protein kinase, is an active kinase in the cell that phosphorylates a number of substrates including several cytoskeletal and signaling proteins. In addition to kinase activity, the ß isoform of CaMKII also contains an F-actin binding region. We recently identified a new F-actin rich structure in developing cortical neurons that endogenous CaMKIIß bound. In nonneuronal cells and dendrite spines of hippocampal neurons where an interaction between CaMKIIß and F-actin has been identified, CaMKIIß was involved in regulating the differentiation of dendrite spines and formation of synapses. In this study, we took advantage of the temporal and spatial regulation of CaMKII isoforms to reveal a specific role for CaMKIIß in binding and stability of a novel F-actin rich structure. We used FRAP and colocalization assays in this CaMKJIß rich system to demonstrate a structural, rather than enzymatic, role of CaMKIIß. In this addendum, we further discuss the significance of this study and the possible implication to the field. ©2009 Landes Bioscience.