Nonexponential kinetics of a single tRNAPhe molecule under physiological conditions.

The fluorescence decay functions of individual, specifically labeled tRNAPhe molecules exhibit nonexponential character as a result of conformational dynamics occurring during the measurement on a single molecule. tRNAPhe conformational states that interchange much more slowly are evidenced by the distribution of lifetimes observed for many individual molecules. A structural model for the nonexponential decay indicates that the tRNAPhe-probe adduct fluctuates between two states, one of which provides conditions that quench the probe fluorescence.