In vivo monitoring of plant small GTPase activation using a F？rster resonance energy transfer biosensor

Mechanism of Raichu-OsRac1 FRET sensor. Raichu-Rac1 consists of the fluorescent protein Venus (yellow), the CRIB domain of PAK (grey), the small GTPase Rac1 (red) and the fluorescent protein CFP (cyan). When OsRac1 is bound to GDP, the intramolecular association between the CRIB domain of PAK is weak, and fluorescence of 475 nm thus emanates from CFP upon excitation at 433 nm. When OsRac1 is bound to GTP, intramolecular interaction between the PAK CRIB domain and OsRac1 brings CFP and Venus into close proximity, causing FRET and fluorescence of Venus at 525 n