LINKER FOR UNIMOLECULAR FRET BIOSENSOR BASED ON PRINCIPLE OF FLUORESCENCE RESONANCE ENERGY TRANSFER
[Problem] To provide a linker for a unimolecular FRET biosensor, as well as a unimolecular FRET biosensor and such generally containing a linker, which enable the measurement of non-invasive serine-threonine protein kinase activity, tyrosine kinase activity, and small GTP-binding protein activity, and are based on the principle of fluorescence resonance energy transfer. [Solution] Provided is: a linker that is a polypeptide containing between 52 and 400 amino acid residues, with at least 95% of the total number of amino acid residues comprising glycine, serine, threonine, and alanine, and which contains 35-65% of glycine, 10-40% of serine and/or threonine, and 10-40% of alanine
unimolecular FRET biosensors mostly containing linkers
a transformed cell which holds an expression vector containing a gene which codes the biosensors
and a transgenic nonhuman animal.