Patent ID: 8426138

Claim:
A method of detecting translocation of a cell-surface receptor to an endosome, said method comprising: (a) providing a cell comprising: (i) a first fusion protein comprising a cell-surface receptor and a first β-galactosidase fragment; and (ii) a second fusion protein comprising an endofin FYVE domain that localizes to a phosphatidylinositol-3-phosphate-containing endosome and a second β-galactosidase fragment; wherein said first and second β-galactosidase fragments complement one another to produce an active β-galactosidase enzyme when in close proximity, and the second β-galactosidase fragment is altered by an amino acid substitution in a region from amino acid residue 29 to 41 of the wild-type β-galactosidase sequence such that the first and second β-galactosidase fragments have a reduced affinity for each other as compared to wild type fragments; and (b) evaluating said cell for active β-galactosidase activity to detect translocation of said cell-surface receptor to said endosome.