Photonic Resonance Energy Transfer (image) University of Miami Caption Photonic resonance energy transfer described by Förster, or FRET, occurs when two small proteins come within a very small distance of each other -- eight nanometers or less. The fluorescence lifetime of the donor molecule will become shorter -- from 3 nanosecond to, perhaps, 2.5 nanoseconds. We then interpret this as evidence that the two proteins of interest are physically interacting with each other -- a molecular signaling event. Credit Akira Chiba/University of Miami Usage Restrictions Must be used with credit. Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.