Patent ID: 8101373

Claim:
An in vitro method for determining the effect of an intracellular environment on the binding of first and second proteins, where said first protein is fused to an enzyme donor fragment and said second protein is fused to an enzyme acceptor fragment, said enzyme acceptor and enzyme donor are fragments of β-galactosidase and said enzyme donor fragment is one of (a) X 1 -X 2 -X 3 -X 4 -V-V-L-Q-R-R-D-W-E-N-P-G-V-T-Q-L-N-R-L-A-A-H-P-P-F-A-S-W-R-N-S-E (SEQ ID NO:6), (b) X 1 -X 2 -X 3 -X 4 -V-V-L-Q-R-R-D-W-E-N-P-G-V-T-Q-L-N-R-L-A-A-H-P-P-F-A-S-W-R-N-S-E-E (SEQ ID NO:7), or (c) X 3 -X 4 -V-V-L-Q-R-R-D-W-E-N-P-G-V-T-Q-L-N-R-L-A-A-H-P-P-F-A-S-W-R-N-S-E-E-A-R (SEQ ID NO:9), wherein X 1 is D or is absent; X 2 is S or is absent; X 3 is L or is absent; and X 4 is A or is absent; said method comprising: exposing said proteins to said environment in vitro; adding to said proteins a β-galactosidase substrate providing a detectable signal; and determining said signal, where said signal is related to the effect of said environment on the binding of said first and second proteins.