Patent ID: 7029868

Claim:
A method for determining fusion between two cell types via the measurement of fluorescence resonance energy transfer (FRET) comprising: (a) providing a first cell that expresses β-lactamase; (b) providing a second cell that does not express β-lactamase but contains a fluorescent substrate of β-lactamase where the substrate is a compound comprising two fluorescent moieties that are connected by a linker that is susceptible to cleavage by β-lactamase where the emission spectrum of one moiety overlaps the absorption spectrum of the other moiety and where FRET can occur when the linker is intact but does not occur when the linker has been cleaved; (c) measuring the amount of FRET from the substrate in the second cell in the absence of fusion between the first and second cells; (d) bringing the first and second cells into contact under conditions such that fusion occurs; and (e) measuring the amount of FRET from the substrate after fusion has occurred; where the ratio of the amount of FRET measured in step (e) to the amount of FRET measured in step (c) represents the amount of fusion that has occurred, with smaller ratios indicating greater amounts of fusion.