ApoE constructs were generated to express YFP and CFP at the N and C termini, respectively, to act as reporter FRET fluorophores. When expressed in Neuro-2a cells, YFP-apoE4-CFP displays significantly more FRET signal compared to YFP-apoE3-CFP-expressing cells. This reflects the closer interaction between the N- and C-terminal domains in apoE4 and demonstrates that the biophysical property of domain interaction occurs in cells (Xu et al., 2004). Modified from Figure 1, Xu, Q., Brecht, W.J., Weisgraber, K.H., Mahley, R.W., and Huang, Y. Apolipoprotein E4 domain interaction occurs in living neuronal cells as determined by fluorescence resonance energy transfer. J. Biol. Chem. 279: 25511–25516, 2004. © the American Society for Biochemistry and Molecular Biology.