Patent ID: 7855072

Claim:
An isolated nucleic acid comprising sequence encoding a chimeric protein, the protein comprising at least one signal protein that has a trafficking signal targeting to a subcellular organelle or plasma membrane and at least one proteolytic cleavage site for a protease, which is constructed such that (a) the trafficking signals of all the signal proteins are inactivated by linking the proteolytic site or a signal masking protein through the proteolytic site to the N- or C-terminus of the signal proteins and thus the chimeric protein is present in cytosol; b) the trafficking signal of at least one signal protein is activated when the proteolytic cleavage site is cleaved by the protease and as a result at least one fragment protein that includes the activated signal protein and at least one detectable amino acid sequence is transported to the subcellular organelle or plasma membrane; and c) the chimeric protein is labeled with the at least one detectable amino acid sequence and the position and intensity distribution of the detectable amino acid sequence signal in the cell is altered depending on the cleavage by the protease, provided that when the detectable amino acid sequence is targeted to the plasma membrane, it remains on the plasma membrane or is translocated from the plasma membrane to the cytosol.