Fluorescent nucleotide analogues

The present invention provides fluorescent cyanine dye-based nucleotide analogues, in which the cyanine dye is coupled to the γ-phosphate group of a nucleoside triphosphate. Preferred embodiments of the invention are directed to fluorescent cyanine dye-based GTP analogues which may be employed in an homogeneous FRET-based assay to measure the binding of guanine nucleotides to GPCR polypeptides, or alternatively, to measure the effect of an exogenous ligand on GPCR protein binding.