Patent ID: 7300762

Claim:
A method of determining the cellular and/or extracellular localisation of a protein of interest comprising: i) introducing into a cell a nucleic acid molecule comprising a nucleotide sequence encoding a modified Green Fluorescent Protein (GFP) fused to a nucleotide sequence encoding a protein of interest, said nucleic acid molecule being operably linked to and under the control of a suitable expression control sequence; ii) culturing said cell under conditions suitable for the expression of said protein of interest; and iii) determining the cellular and/or extracellular localisation of said protein of interest by detecting the fluorescence emission by optical means; wherein said modified GFP has the amino acid sequence of SEQ ID NO: 2 except for: a) an amino acid substitution at position F64; b) a single amino acid substitution at a position selected from the group consisting of positions S65 and E222; and c) an amino acid substitution at position S175; wherein said modified GFP has a different excitation spectrum or a different emission spectrum compared with wild type GFP or has a different excitation spectrum and a different emission spectrum compared with wild type GFP.