Provided, based on the principle of a fluorescence resonance energy transferis, a linker for a unimolecular FRET biosensor, as well as the unimolecular FRET biosensor and such containing the linker, which can measure non-invasively a serine-threonine protein kinase activity, a tyrosine kinase activity, and a low molecular weight GTP-binding protein activity. The linker 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 wherein 35-65% of glycine, 10-40% of serine and/or threonine , and 10-40% of alanine are contained; the unimolecular FRET biosensor mostly containing the linker, a transformed cell which holds an expression vector containing a gene which codes the biosensors and a transgenic nonhuman animal are also provided.
Linker for unimolecular FRET biosensor based on principle of fluorescence resonance energy transfer