Fig. 1
From: One pattern analysis (OPA) for the quantitative determination of protein interactions in plant cells
FRET and BiFC can be used to investigate protein–protein interactions. A FRET describes the process of non-radiative energy transfer from an excited “donor” fluorophore to a non-excited “acceptor” molecule. Occurrence of FRET depends on three specific conditions: (i) the emission spectrum of the donor and the excitation spectrum of the acceptor must sufficiently overlap. (ii) The orientation of donor and acceptor dipoles must not be oriented perpendicular to each other. (iii) Donor and acceptor molecules must be in close proximity towards each other (< 1 nm or 100 Å distance). B BiFC is based on the complementation of two fragments of a fluorescence protein (FP). Fluorophore functionality is regained when the fragments, fused to interacting proteins, are brought in proximity to each other. C Combination of BiFC with FRET allows to investigate larger protein complexes. Thereby, the complemented FP can serve as a donor or acceptor