The nonhydrolyzable nucleotide BODIPY® TR GTP-γ-S has the fluorophore linked the the ?-thiol of GTP-γ-S. The fluorescence of the BODIPY® TR GTP-γ-S thioester is quenched ~90% relative to that of the free dye but is recovered upon protein binding to at least some G-proteins. BODIPY® TR exhibits spectral characteristics similar to the Texas Red® dye.