A neuronal immediate early gene Arc is rapidly induced in response to synaptic stimulation, and its mRNA is transported from the nucleus to the activated regions of the primary dendritic shafts (Layford et al., 1995). Furthermore, Arc protein associates with cytoskeletal proteins and accumulates in the postsynaptic density. We previously showed that Arc directly binds to several postsynaptic proteins including CaMKII and PSD-95 (Chowdhury et al., SFN Annual Meeting 1999, 2002). To further investigate Arc-CaMKII interaction, we measured fluorescence resonance energy transfer (FRET) between CFP-tagged Arc and YFP-tagged CaMKII pairs. A screening system that combined random insertion and yeast 2-hybrid (Y2H) assay was developed to obtain optimal FRET pairs. GFP variants were introduced into Arc and CaMKII using transposon-based gene insertion, and fusion proteins that maintained the integrity of Arc-CaMKII interaction were screened using Y2H. Optimal pairs were then selected based on FRET efficiency in COS ce...