pEBFP-C1 carries a blue fluorescent variant of the Aequorea victoria green fluorescent protein gene (GFP). The EBFP gene contains four amino acid substitutions. The Tyr-66 to His substitution gives EBFP fluorescence excitation and emission maxima (380 and 440 nm, respectively) similar to other blue emission variants. The other three substitutions (Phe-64 to Leu; Ser-65 to Thr; and Tyr- 145 to Phe) enhance the brightness and solubility of the protein, primarily due to improved proteinfolding properties and efficiency of chromophore formation. The Em of EBFP is 31,000 cm–1M–1 for 380-nm excitation, leading to a fluorescent signal that is 2–3-fold brighter than other blue variants of GFP and roughly equivalent to wt GFP. In addition, the rate of photobleaching of EBFP is one-half to one-third that of P4-3, a popular predecessor to EBFP. EBFP contains >190 silent mutations that create an open reading frame comprised almost entirely of preferred human codons .
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