Yellow fluorescent proteins spectra

FRET requires the presence of two fluorophores, one with a shorter emission wavelength (donor) and another with a longer emission wavelength (acceptor). The fluorophores must be chosen such that there is sufficient overlap of the donor emission spectrum and the acceptor excitation spectrum. When FRET occurs, which requires the proximity of the two fluorophores, excitation of the donor results in transfer of energy to the acceptor and, hence, emission at the wavelength characteristic for the acceptor. FRET can be seen with various kinds of fluorophores, but most recendy it has been used in particular with variants of GFPs because this permits FRET in intact cells. The most frequently used pairs of GFPs are the cyan fluorescent protein (CFP) and the yellow fluorescent protein (YFP) variants. The donor CFP is excited at its maximum... 

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